I had Dinan S2 on my 2008 E60 535xi. The power (increased of 90hp & 120lbft tq over stock) is amazing and I did not experience any problem with the flash at all. Got it done at Budds BMW Oakville.
Then this past summer, I test drove the 2011 550i and in comparing between this & my (Dinan flashed) 535xi, it felt like my 535xi has a much stronger push of power when it hits about 4K - 5K RPM but the power delivery of the 550 is extremely smooth right across all RPM which I much prefer.
Therefore, I bought the 2011 550x drive by saving the hassle of having it tuned. Of course, I can always get it tuned by Dinan again for $3000US + HST + Labor = $3700 ... too steep for my pocket (for now) ! The only pain is every time the dealer worked on the car which involves updating the ECU software, it simply wipes out the Dinan flash and I would have to wait another 1 - 1.5hr more for them to do the reflash.
Last edited by bobblehead; 11-19-2010 at 08:41 AM.