I used them on my 2-wheelers and now on the Freewheeler. I got foot issues; so, it sort of became a must for me. I even installed one on the brake pedal of my 48 - back when I was able to ride it.
....And, the cover is a hard plastic, not rubber, so....I think the tennies will be safe and mark-free.
I have to say that I have seen a lot of folks use them; and, I am surprised HD never made something like it......
Now, for me, I am not one for a heel-shifter. So, I removed mine and bought HD's $45,000.00 chrome cap to cover the end of the shift spline.
.....OK, I may be off on the exact cost of that cap......
Anyway, great mod and a great write-up!
Thanks,
Springman