After a few years of heavy use, I was looking for something to replace my M-Audio Code 49 and the aim was to upgrade to something more premium/professional (I use my controller every day, for several hours).
The two main contenders were the NI Komplete Kontrol and Arturia, but I opted for the latter in the end as for my needs the integration and workflow are superior, but your milage my vary.
First; the build quality is top notch. I come from a background of hardware synths and this is as close as a MIDI controller will come, there are moments where I forget this is a controller and not a really well made synth. The aluminum body feels great, the pitch and mod wheels also have a very nice feel. Knobs feel good to press, with just enough resistance and "click" and the layout of controls is very ergonomic for me, but again your milage my vary.
Encoders and faders are good, the latter have a good feel and the travel is smooth, however both of those are a noch bellow the rest of the stuff, but not bad in any way.
What wins for me is the integration with AnalogLab and the V Collection, which I have been using for a very long time; the workflow is absolutely worth the money in my opinion. It delivers the hands-on synth experience and sound-design becomes a delight. The transpose function is well implemented (just press the "transpose button" and press the desired key), pads feel nice and I love the chord mode on them.
The only divisive aspect of the Keylab MkII might be the keybed; before I tried it, I heard both a lot of good and bad stuff about it and to be honest BOTH are true in a way... From a synth perspective, this is an absolute breeze to play, the aftertouch is responsive and one can absolutely fly over the keybed with leads and bass lines. It is a very nice synth action keybed and I wouldn't mind something akin to this on some of the hardware synths.
On the other hand it is a synth action board (a very good one IMO), but for piano and orchestral sounds, the board might not be perfect; I still use the Code for some of that stuff as it has semi-weigthed keys and I'm still used to that a lot. Again, it comes down to personal preferences. The mod and pitch wheel are also quite small, so using them for dynamics of orchestral plugins can be a bit jarring at first.
With all that out of the way, I can absolutely recommend the board for synth and sound design stuff, which I do mostly anyway and there the Keylab absolutely shines! The integration alone + the fact that the AnalogLab comes included is well worth the price, the build quality is the icing on the cake.