CME Xkey 25 / 37

Sources split, and it's the decision. The majority — most magazine tests and most owners — find the full-width, 2–3 mm chiclet keys fast, forgiving and surprisingly playable: repeated notes and trills are easy, beginners and non-keyboardists get around them quickly, and the poly aftertouch is real and usable once the curves are set. The same sources concede the ceiling: the travel is too short to control dynamics like a real keybed (Bonedo's MIDI-sniffer test found a ~30-value velocity spread at constant effort — about four dependable levels), the black keys sit nearly flush with the whites (barely raised, a touch more so on the 37), so playing blind is hard, and the keys clack like a laptop. A real minority never adapts — Elektronauts' thread has owners who 'hate the keys' and a Reddit pianist who 'tried very hard' and could not — and three separate owners describe individual keys reading low or inconsistently even after per-key sensitivity edits. Aftertouch triggers almost immediately by default (the editor can delay its onset). No release velocity. The 37's raised black keys and extra octave are the version pianists cope with better.

Sources split, leaning critical. There are no wheels, knobs or faders — six rubber buttons: octave ±, sustain, and pressure-sensitive pitch-bend ± and modulation that send continuous values by how hard you press. Octave and sustain are fine (though the 25's sustain must be held down, tying up a finger). The pressure buttons divide reviewers: Bonedo, Keyboardist, Audio Mentor and a Sweetwater owner say they work well once you learn the light touch, and one owner notes they're even velocity-sensitive; Sound On Sound, MusicRadar, DJWORX and several owners find holding an intermediate pressure a lottery, modulation snaps back to zero on release, and MusicRadar calls real accuracy 'pretty much impossible'. The 37 (and the Xcable) lets you plug in real sustain and expression pedals, which is how most players sidestep the buttons.

The strongest agreement after portability: it is a class-compliant USB MIDI device that needs no driver on macOS, Windows, iOS/iPadOS (via a camera adapter), Android or Linux, and every reviewer and owner — including the critic who returned an ESI 37 — reports it working the moment it's plugged in, with Bitwig, Logic, Cubase, GarageBand and hardware synths alike. There is no DAW-specific auto-mapping because there is nothing to map: no transport, knobs or pads, just notes, aftertouch and six buttons. The honest caveats are old and small: a 2014 owner needed weeks to get Windows 8.1 happy, one firmware update required a re-plug, and changing the MIDI channel from the hardware (octave buttons + a key) only works once enabled in the editor. ESI's relaunch adds a Windows multi-client MIDI driver for those who want it.

“Xkey-Controller per USB-Kabel anschließen (über das Apple Camera Connection Kit ist auch ein Betrieb am iPhone/iPad möglich, Android ebenfalls) und dank class-compliant kann es direkt losgehen.”

Felix Thoma · Amazona

“The keyboard is plug and play, being up and running within a couple of minutes of being lifted out of the box.”

Keyboardist

“This keyboard IS thin, it IS light, and it DID instantly work with anything I plugged it into (including Bitwig).”

Malcolm M. · Amazon verified purchase (ESI Xkey 37)

Mostly praised. The free editor (CME's Xkey Plus for iOS/Mac/Windows; ESI's Xkey editor for Windows and macOS 11–15) is the thing that makes the keybed liveable: draw your own velocity curves, set sensitivity per key and per button, scale or delay the aftertouch or switch it to channel pressure, reassign every key and button, and update firmware — all stored in the unit. Reviewers call it decent to exceptional and owners routinely say the keyboard only clicked after tweaking the curves. The dissent: DJWORX found it unfriendly for beginners, Bonedo's iPad curve-drawing was flaky, a 2014 owner called it buggy, and one 2026 ESI-37 buyer returned the unit believing the editor was Windows-only. The ESI bundle (Bitwig Studio 8-Track, Cubasis LE, WaveLab LE) is new since 2024; CME-era units came with at most a Cubasis LE licence.

“One of the really good features of the original Xkey model was the extent to which you could customise its performance parameters using the Xkey Plus support app.”

Dave Lockwood · Sound On Sound (Xkey37)

“The CME Xkey is by far the most versatile and customizable portable MIDI controller I’ve put my hands on and I think it’ll beat most portable MIDI controllers in the market.”

Reuben Chng · Audio Mentor

“However, the app is a little difficult to navigate for beginners and comes with a warning to leave well alone unless you know what you’re doing.”

Hatty Settle · DJWORX

Sources split, and the split is a generation line. Everyone agrees on what's there: one USB port that carries MIDI and power (class-compliant, bus-powered, low draw — fine off a phone or tablet), and on the 37 the Xport socket whose included Xcable breaks out a 5-pin MIDI output plus sustain and expression jacks, so it can drive hardware without a computer. Reviewers treat the 37's breakout as the feature that makes it a real instrument, while the 25 is USB-only with no pedal jack (Amazona calls that omission incomprehensible). The critical camp is about the port itself on CME-era units: a micro-USB socket recessed so close to the housing that only CME's slim-plug cable fits, that owners have bent, loosened and broken — the single most-repeated complaint across every forum. ESI's 2024 relaunch replaced it with USB-C, which Synth Anatomy and Amazona both call the fix; the Xport breakout is also reported as a loose fit.

Unanimous, and the reason the product exists: 16 mm thick, 600 g (25) or 880 g (37), aluminium, bus-powered with a tiny draw, so it lives in a laptop sleeve or backpack and runs off an iPad or phone. Reviewers keep it permanently in front of the monitor as much as they travel with it. The only qualifications are physical: the 37 is too long for airline hand-luggage rules and some backpacks (the 25 isn't), Bonedo wouldn't carry either unprotected for fear of things lodging under the keys, and the wired models have no battery, so 'portable' still means plugged into something. Amazon's owner tally on portability is 25 positive, 0 negative.

“The original 25-note Xkey remains an ideal size for music on the move, as you can fit it in a rucksack or a large laptop bag, and you can operate it on your knees while sat next to someone without getting too antisocial.”

Dave Lockwood · Sound On Sound (Xkey37)

“First, you really can't find anything this thin. I keep it in my laptop backpack I drag into the studio and forget it's even there.”

Havok · Sweetwater customer review (Sept 2021 archive)

“Und fürs Handgepäck im Flieger ist das Xkey 37 im Gegensatz zum ursprünglichen Xkey zu groß.”

Sebastian Berweck · Bonedo (Xkey 37 test)

Sources split, mostly by generation. The chassis is praised by every editorial and most owners: a brushed-aluminium top on a plastic base that feels premium, rigid enough at both lengths, with keys that don't wobble and rubber feet that hold it still. The other camp is about the weak points: on CME-era units the recessed micro-USB socket has come loose, fallen apart or snapped the cable off inside for a string of owners across Gearspace, Loopy Pro, Reddit and Amazon (one unit binned, one repaired by prying open a glued back and finding half the internal screws loose); the keys clack audibly; the board flexes slightly when you lean on it for aftertouch; and a few owners report a key sensor drifting low, or a unit dying after five years. The 2024 USB-C port removes the most common failure, and CME's support drew praise for replacing a damaged unit out of warranty.

Sources split. At its 2013–15 launch prices ($99 / $199, £89 / £149) magazines called it affordable and 'very reasonable', and owners still describe used units at ~$100 as a great buy even in 2026 — the case for it is that nothing else puts polyphonic aftertouch and full-width keys in a 16 mm, 600 g package. The case against was made first by Bonedo, which called the 37 by far the most expensive three-octave keyboard with comparable features, and it has strengthened: the ESI relaunch lists at $179 / $299 in the US (€149 / €249 at the 2024 launch, €159.90 / €269.90 RRP by 2025), around 80% above the CME launch prices, while Arturia's KeyStep 37 and MiniLab 3 undercut the 37 and add knobs, an arpeggiator or sequencer and a conventional keybed. Whether that's worth it turns almost entirely on whether you need poly aftertouch and the thinness; Delamar (on the ESI 25) still rates the price-performance good.