Roll pins are hollow, and brittle since they're spring steel. One overly-energetic shift can break a pin off and drop the broken piece down the shift tower where it will go through those expensive gears like a meat grinder.

Other than that, a roll pin fox is quick, easy, and WRONG! "Other than the iceberg, how did you like the trip on the Titanic?"
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!