Hi,
I have both a Yak Comp Arf and a Krill Velox. Building wise, the Comp Arf is a little easier to put together since items are clearly marked. If you have experience, both planes will be straight forward to build. The Krill comes with 300 pictures on a cd that you should study before assembly. Landing gear on a Krill is much better than a Comp Arf. Fire wall and tail assembly is better on a Comp Arf. The Krill is lighter and takes a large variety of engines and has space for them. If you are running cans, the Comp Arf is better since they run on the outside which I like.