Dianan is always more expensive. Really folks...this is a BMW, not a f-ng STI or Honda rice rocket.
Warranty itself should be worth it's weight in gold. Afterall, what to u think all the piggybacks out there would have cost you if they offered their own warranty as well???
IMO, all of you with the 335i are being short sighted on this. Until now you were #1 stuck with a stock oil cooler that most people can agree is not sufficient for prolonged heavy track use, #2 stuck with stock flow rate on the h2o pump. Worst case with Dinan's release is that you now have options.
Dinan warranty: I believe it's a piggyback warranty. There is a chance that you could possibly be caught between Dinan and BMW on a warranty claim, but I have yet to hear anyone of ever having to go through that.
Dinan products are installed AT BMW dealerships by BMW Techs.