I was looking for a compact keyboard to be on top of my desk, 37 keys was good enough, as all 49 keyboards I came across were to big for my desk.
The new launch key mk4 is great, compact enough for my needs, but without compromising keybed feel - which is great for a keyboard of this price and size, and the most important aspect for me.
All other functions are cool too (Arp, Scale and Chord Map) but fixed chord is great - it lets you record your own voicing on to the pads and play them when you want. This is a great feature if, like me, you're not a piano player and you can't change between chords fast enough, or you have some difficult/weird voicing you want to play.