I’ve got mixed feelings about them. I moved from Vs to BB5s and then BB7s. Initially I found them great with lots of stopping power and fairly easy to set up but they come across as a bit ‘cheap’ (I’ve got 2008s which seem a fair bit cheaper than previous year’s models), the plastic adjuster knobs tend to round of (just plastic over a metal spindle) or drop of and I’ve noticed a fair bit of wear. On a couple of my calipers the knobs on the pistons over which the pads fit have worn/broken off. I also noticed a fair bit of ‘pulsing’ with on the front brake (although I’ve heard comments that this may be down to the wavy Avid Roundigon rotors rather than cable discs).
I also found pad removal/fitting a real faff (although to be fair I’m notoriously ham fisted). I’ve recently had a BB7 start to jam as the arm became slackish and now wedges itself against the caliper and I’ve failed to resolve it (I’ve ordered a replacement though as it’s cheaper than a new set of hydros).
That said BB7s have served me really well as an introduction to disc brakes and I went for cables as I was feeling nervous of hydraulics. Having upgraded my main bike to hydraulics I wouldn’t go back though.
I also think that you need to look in terms of price for price, an Avid BB7 is around £40, so £80ish for a pair plus cables and levers, I upgraded to Deore LXs, which I feel are much better brakes, for £105 (including levers) and you may be able to get Deore hydros. for less. I don’t think that I’d go back to BB7s.