My dad had a Harley rake, but never a Harley picker.  What we disliked about Harley at the time was trailer was pulled behind the picker, so backing up to a rock pile was quite a job.  Think about how tough it is to back up a 4 wheel trailer being pulled behind a 2 wheeled picker. 

Lots of moving parts to wear out too, especially the conveyer chains.  As to not working in corn stalks, I've never seen a picker of any brand that did work in corn stalks, except maybe the two legged kind.

One other thing, they DO NOT work going down hill.  The rocks won't move out of the drum fast enough.