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they wouldn't have been around for over 20 years unchanged if they weren't decent brakes.
You can still buy rod brakes and cantis unchanged and they're shit but they've been superseded. BB7s are fine however especially if cable discs is what you need, they're one of the few things still branded Avid and the mounting hardware makes up for poorly faced disc tabs. The red bits usually survive ok if you don't polo and they're cheap to replace.
Really is nothing to worry about, they wouldn't have been around for over 20 years unchanged if they weren't decent brakes.
Take the time to sort them up per here :
http://howtosetuptheavidbb7.weebly.com/how-to-set-up-the-avid-bb7.html