Bryan I actually attended BYU (was raised LDS but am no longer practicing). Happy to directly address any BYU questions although I think you summarize it pretty well :-). Masturbation is definitely frowned on but not nearly to the extent of pre-marital sex (thus all the young marriages). I did not encounter anyone there in a chastity belt but the power of religious guilt alone is pretty effective in terms of influencing behavior...
It is interesting for me to observe a society in which they actually practice chastity, that is willingly abstain from sex. Unlike this forum where the large majority - but not everyone - do not practice it, they are forced into a belt and that's what keeps them "chaste".
I observed the girls we ran against with great interest. They may be chaste but are definitely NOT old maids. They keep their bodies in good condition, are well made up and, in hot weather, ran and allowed themselves to be photographed in short shorts and bare midriffs, running gear, that is, not some sort of sexualized outfits.
The reality of a chaste life is far dififferent from the kind of patriarchal/matriarchal crap you read here where people seek to deliver their daughters intact to their future husnands by any means necessary.