The Rio items were not as smooth and had much sharper edges than the Empeg did and one of the hooks on the handle fouls the sled which stops the handle from folding down fully and also doesn't allow the player to lock itself into the sled.

I'm having this problem too. I'm now using a Rio60, but my first Rio was a Rio10. I'm still using the sled of the Rio10 in my car. But somehow, the Rio60 doesn't "click" as good in the sled, resulting in the player sometimes "ratteling" when driving. Pushing the handle stops this, but the problem comes back when the road I'm driving is bumpy.
I guess I could pry something under the handle to have it lock more sturdy, but I haven't come around to it yet.