BB7 are a fave because they are cheapish and easy to deal with and effective at what they do.
But, disc brakes really have nothing to do with safety in most conditions. They do not stop you any faster than properly set up v-brakes in most conditions.
jim
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Cross Check Nexus7, IRO Mark V, Trek 620 Nexus7, Karate Monkey half fat, IRO Model 19 fixed, Amp Research B3, Surly 1x1 half fat fixed, and more...
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SB forever