IK Multimedia iRig Keys I/O 49

TL;DR: If you work solo, need portabilty + playability, and aren't picky about 'weighted keys' - this is a good choice.

For a hobbyist singer/songwriter/producer like me it is just the ticket. I am not a piano player, so I don't miss any weighted keys and such - action here is pretty satisfactory for unspoilt hands of the guitar player. And it is so much better than micro 32 and 37 keys I own! Gives you a real feeling, making you actually want to play for fun, not just input notes and build chords into a DAW. Not on par with a Novation I once had, but for this price? A no brainer!
And no complaints about it being plastic-y - c'mon guys, who really wants metal and / or wood in their hand luggage?
Having the interface built-in is super convenient where space and weight is an issue. Unlike some YouTube reviewers I haven't yet experienced any problems with latency / dropouts (buffer set at 128 samples). On the other hand, I didn't try to run a 40+ tracks projects with loads of VSTs and effects thru it: it is something I do at home on an iMac and a Focusrite.
One combo input for audio is also fine for me - a scratch track can easily be done with miked acoustic guitar + voice, and when it comes to proper recording, I do all tracks separately anyway. So, if you're solo, and don't need to record your jam with a friend, no problem here.

I use this on an iPad with GarageBand and on an iMac with Logic. The keyboard is just the right size for those with limited space, and it's easy to pick up and move between the iPad and the iMac. The keys are very playable with good velocity response. The letdown in this is the audio interface. It's fine for use on the fly with the iPad, but working with more than a few audio tracks there is not much clarity and playback can become choppy. You can change some parameters (buffers etc.) within your DAW to mitigate this somewhat. Again, perfectly fine for getting something going on the iPad but I find myself switching to a more capable, dedicated audio interface (FocusRite) when using the computer.