I have had nothing but great experiences with OE tuning. I dropped my JB3 for their tune on my e60 535i and never looked back. There was more power, smoother delivery and it was completely invicible to the dealers.
I know that because I had numerous issues worked on the car with not one worry about my warranty. I never tried to hide the tune by uninstalling it, just dropped the car off as is.
2012 535i M-Sport
Previous BMW's: 87' 528e / 04' 325i / 07' 335i / 08' 335i / 08' 535i