I received mine today (version v2r0) and it's a bit pants really :/
Horizontal movement is super nice and the vertical one is too but only when it works as it should.
If I move the mouse in one direction, stop for a bit, and then move the mouse in the opposite direction the cursor will travel a bit in the previous direction before changing and going the correct way. This only happens on the vertical axis but it's obviously super annoying so this kit is going in the bin - or well, I'll fire off an email first to check if they've tested these things on actual Ataris

It's a pretty simple board with just an ADNS-9800 and a PIC microcontroller and I must assume they have a bug in the PIC software.