I have had the intercooled ESS S/C kit for over a year and have had no issues. I have tracked the car and the temps have been normal at all times. The reliability of this kit speaks volumes for its tuning, craftsmanship and design. It just works!
As for the dealer questions, I speak to the service manager before I take my car to a new dealer. After a quick conversation they let me know which service advisor to work with and then we are all set. I have had warranty work performed no problem.
... and the BBK. It would help, but it is not required. I mean if you track the car you will need to get some track pads for the stock brakes or a BBK would greatly help.
The added power in the car is just amazing! I have a smile ear to ear every time I drive it. When I give people rides they are amazed how fast the car is and how hard it pins them in the seat. I could not imagine my M3 without it now!
I would highly recommend the ESS S/C for your M3. I hope this helps!