I used "Ultra-Thin" Grab-ons on my racing bike in the mid-eighties. They are dense closed-cell foam of a reasonably high durometer, not too squishy. I put cloth tape over them of course, I'm not a
total fred. I didn't get ostracized by the other racers (especially on the odd occasions when I won), in fact I don't remember anyone even noticing them.
They're very durable, essentially never wear out if you keep an intact layer of cloth tape over them. I used to move them from bike to bike (bar to bar) rather than sell the bike with them still mounted. I still have some used ones waiting for the right bike, and a NIP set that I set aside and then lost... and then found.
Grab-on co-sponsored a top US team (with Davidson) for a while, probably around '78-'82. Their best racer was Mark Pringle, who used to beat George Mount and young amateur Greg Lemond at least once in a while (in case you hadn't heard of him). He's still the answer to the trivia question "what's the best placing ever by an American in the World Amateur Men's Road Race Championships". Mark got 10th in '79. Second best was Lance Armstrong who got 11th before he turned pro.
Whoops looks like Jacques Boyer was also on Team Grab-on. I guess even as a Pringle fan, I'd give the nod to Boyer as the better racer. Pringle never turned pro, that I know of.
No racer would be caught dead with the thick ones though!