I don't have any experience with Performance so I can't say good or bad things about them other than what I've seen online.
I've been dealing with Mark Aliano @ Leith BMW since I got my car and haven't had any problems. My HPFP actually went out the day I had my exhaust installed - no warning signs just a long crank and immediate check engine/half engine light that afternoon. When I took it in I told them that I had just installed an exhaust that morning and at lunch I had a very long crank and immediate CEL. They agreed that the 2 shouldn't/couldn't be connected and took a look at it and determined it was the HPFP and replaced it under warranty same day - no questions asked and no hassles about the exhaust. They also don't seem to care about the Injen intake. Of course I've also made it very clear my car isn't tuned and probably won't be unless I get a 2nd car and/or my warranty expires.
On a side note when I had to send my exhaust back to CP-E to have the stealth pipe welded on I actually stopped by Leith and got the box to ship it in - they walked me back showed me the boxes they had and said take your pick.
