As for road tests, well, upshift is easy, smooth, immediate. Haven't had a slip out since I've done it.
Downshift, that's another story.
Because this shifter is mostly straight, the end of the lever needs to roll toward your heel when you push it down, the rubber booty sticks to the bottom of your boot making the angles and forces needed a little funky.
You get used to it but it's not ideal and still bother me a bit.
I think this design would be ideal:
But I don't have the facilities to make and test one to be sure. it's just a sketch from my head... I haven't been able to find an actual shifter in this shape.