derailleur protectors

[saturnsc2]

does anybody use these? how do they attach to the bike? i seen a cheap wal-mart mountain bike the other day & it had one of these over the rear derailluer, but i didn't get a real close look at it though. i wonder why my very expensive mountain bike don't have this. recently my mountain bike fell over & nicked the rear derailluer a little. can these be put on any kind of bike, or just mountain bikes?

[RC2]

Assuming you have a POS, overbuilt/heavy frame and that the rear derailleur is potentially worth more than your frame, this approach is fine.

If you'd rather replace a derailleur in the event it gets gimped to the extent it can't be fixed and save your frame, skip the protectors.

Besides, they just don't look cool!