I was lucky and found a great deal. The JCW
brake package and the new disc and pad upgrade was still a lot cheaper for me that the £650 you mention.
And i can keep my warranty.
When we changed over the discs and pads etc we measured everything up and all the parts were the same sizes.
I have heard the main reason for the comments about incompatibility was because of branding and they had to make out that they were different because of this reason.