PROS: the integration with Ableton Live is great! As far as I know, at this price range, that's the best you will find. Other features like the arpeggiator and chord memory are also very useful regardless of your DAW. The MIDI out is another plus.
CONS: the build quality is awful, especially the keys. They have a terrible wobble to their sides, it feels like they will break at any moment, even though probably (hopefully???) they won't. The rotary knobs on top are just ok, a little wobble as well as you might expect from a cheap piece of gear, but nothing extreme. The major downside is that there is very little space between them. Regarding the pads, they do their job, even though they are quite small compared to other controllers.
VERDICT: Previously I've owned a Minilab and an AKAI MPK mini and by far the Launchkey has the worse build quality. On the other hand, it has the best integration with Ableton and the best features overall. So I'd say if you're a musician looking for a keyboard to actually play stuff, buy something else. But if you're a producer/beatmaker on a budget, the Launchkey will do the job!