Hmm, no idea but with something as important as your brakes, I'd be a little cautious of the no-name approach.
Run a couple searches in this forum, there have been a few good brake pad/rotor threads in the past 6 to 9 months. I recently needed new pads and rotors in Front and after some research bought all my stuff from Dave Zeckhausen, a board member and sponsor:
If you look at the very bottom product on the page you can see its also a single disc for the E39 M5 and thats at a shade over £200 per disc.
This would suggest heavily that the top listed ones are in fact either unsuitable, single piece, of inferior quality to OEM or in fact a combination of all 3 of the above as why would you sell E39 M5 discs at £100 a pair, and then a single one at double the price?
I think their description of the actual item they are selling should be a little more detailed, if someone put these on their M5 and had to brake hard and the car didn't stop properly because of the inferior discs, who is to blame us for buying them or the company for selling them..??
I think for us in the UK, if not buying the discs (rotors) from main dealers etc then at least you can get them from german & sweedish or euro car parts and these will be either original oem ones or at least come much closer to the performance of the original.
German Swedish don't sell them and Euro Car Parts list them and they are a Pagid disc, but they are pretty much main dealer prices anyways at circa £200 a disc which ties up with the bottom listing from the linked website.
Trust me mate i've been there and done it!!!
You can get them from bmminiparts for cheaper than the dealer but the postage costs with them being so heavy pushes the price up again towards dealer prices so you'd have to order different bits and bobs together to make it worth your while
Sorry never replied before with the links etc.
Well since I posted this thread a long time ago i'll update it by saying that i now know better and would never run aftermarket discs on an M car from any company unless it was a brake kit/upgrade. IMO the pattern part stuff is utter garbage and there's a reason it's cheap.
On another note i have a good supplier of LUK clutches and flywheels if anyones needing to replace theirs, i put up another thread about it a while ago, but contact me if you need more details.