My wife just bought a new bike with disc brakes but they're Avid BB5s or something and they are utterly rubbish. I've got one bike with unbranded calipers that are better than than these, despite trying to dial slack out of them.
My only experience of discs has been Shimano hydraulics on MTBs and they will but you over the bars quick sharp. These mechanical things feel like trying brake with 2 pieces of stale bread or something. You get what you pay for I guess.