I have only bought brake parts from Trent. I bought their "Group N" kit (front and rear) for my 9000 Aero. Graham is an extremely helpful chap.
I would query the price of the "Group N" kit, though. At one time, the specification called for grooved and/or drilled discs and Trent machined these themselves, adding considerable value. Now, however, the Ferodo DS2500 pads included as part of the "Group N" package are said to work best with plain discs and Trent supply standard Brembo discs without any added machining. These are, of course, very good discs. However, I can buy these for half the price elsewhere.
Also, since Ferodo DS2500 compound isn't available to fit the 9000, Trent machine the backplate of a pad that is a close fit (specified for BMW M3 and Ferrari Testarossa), again adding value. Or at least they used to. Whether they have stopped doing it or whether it was an oversight, when I ordered a set of replacement front pads from them, they hadn't been machined and I didn't find out until I was trying to fit the pads.
Having filed them down once myself, I now buy the pads from a cheaper source as well and modify them myself.
Trent deserve some return from developing and testing the "Group N" package and identifying pads that can be modified to fit the 9000 and give great performance. I also have no objection to paying a little extra for pads that are already modified.
However, double the price for selling standard discs off the shelf sounds a bit much and if I have to modify the pads myself, I'll get them from a cheaper source.
If I decide to go for stiffer springs than the Abbott ones I currently have fitted, I'll definitely go back to Trent for their expertise and level of service.