I had the K-2 for quite a long time, and I wanted to make sure I understood how it works, before writing a review, because it has some quirks, in contrast to other more popular Behringer clones. I'd say, although it sounds fantastic maybe you should go with a Pro-1 or a Model-D if this is your first analog synth.
The good parts first: It is well built! The oscillators sound fantastic, and the low pass filters (two switchable types) sound really rich, with the first one, being able to produce some really squeaky sounds once you crank up the resonance. I was blown away by the sound I god right away. Need extra bass? Turn up the resonance of the HP filter and dial in the appropriate cutoff! Awesomeness!
On the other hand, due to cloning the old design, there are some important features missing, like PWM. EG2 behaves strange, and EG1 -although it could be used for many things,its only patched to OSC pitch. On the right side of the device, the patch diagram can get confusing and takes some time to learn. When you do learn it however, you'll be able to do crazy stuff.
It is an elementary addition to your gear, IMHO!