crank_addict

I guess could say that pic is a 'can opener' for discussion.

I don't like or use them BUT, have noticed the many brand new, mid / higher end bikes still come with them. Last year I was out on a group ride and some gal with un-named but better quality CF bike was honking an ascent, next thing she's down. Some how the plastic disc was still on her bike but broken. Baffled and I don't know all the facts but her bike was relatively new that season and the LBS must not have dialed in the derailleur.

(I was able to help, un-mangle the jammed chain mess, snap off the sheared garbage plastic and quick limit adjustment. After the ride and at the shop, I think they might have had to order in a replacement dropout. Which, by the way is a great modern feature!)