I got an Xkey 37. Polyphonic aftertouch only. Pretty nice for $200 and two pounds. Had to install its configuration app to switch it to channel pressure.
I thought the sustain wasn’t working but then realized that when the initial aftertouch value is zero, the note won’t sound when there’s no pressure. D’oh!
Enjoy it! They’re great to just have lying around as spare keyboards, and while the configuration app is a little bit of a pain, they remember their settings and then you’re good to go. The non-air 37 is great fun as a standalone MIDI keyboard with sustain and expression pedals, but I have a 25 Air that goes with me almost everywhere. Big thumbs up, especially for the price; there’s some competition out there but nothing that’s got its combination of portability and playability.