As far as I know there is no difference in the gearbox internals on the 13 with the shift assist.
Most of us did our practice, practice, practice many, many, many years and bikes ago.
I also think there is a big difference in the riding styles of owners at play here. The faster and harder you use the box with a shift assist the better it likes it. Conversely, timid prods at the lever with ottle demand can confuse the poor thing. Much as it galls me to say this, but being brutal with the throttle and the lever gives by far the best results (and of course a huge grin inside the helmet
).
I can guarantee that anyone trying an clutchless upshift with proper advice will get perfection within the first few attempts and the odd crunch never does much harm anyway, we've all missed gears and bolloxed it up before now and never broken the box.