I've been doing business with Cass (DoctorDiff) for years. Some of the parts will be the same as from PirateJack and other sellers, because the ultimate source is the same. For example, I'm sure the replacement spindles all come from the same place. However, the additional parts like, rotors, bearings, brake hoses etc have all been high quality from DoctorDiff, and that's not what you'll get from PirateJack. At least not from what I've seen.
The biggest thing is that if you do have a problem, you can send Cass an email and he'll get back to you and help you sort it out.