I have just found out that the M-Flash is totally undetectable! I asked them and they said they work closely with a BMW engineer and no matter how hard he tried, he could not find any trace of the M-Flash being used!
HOWEVER
I also found out this
The 2009 245ps LCI model we have cannot be tuned through the OBD unlike the pre-LCI 231hp model as it has security (like DRM on a music file). Bummer.
More-BHP (the company in question) have said that they can remap the ECU though to achieve the same results but I would imagine this is very obvious.
"Many thanks for your enquiry about the M-Flash.
No useful evidence stored anywhere. We are friends with our local BMW Master Tech who still hasn't ever been able to prove a car has been remapped, even if the ecu has been opened !
The M-Flash is very well made and extremely reliable, there are a number of 330d out there using the system.
I am assuming your 330d is still the 231bhp model? The newer 245bhp model cannot be done by the M-Flash as the ECU is protected against OBD programming.
The last manual 330d 231ps that was dyno'd independently made 308bhp and 680Nm on "race" programming. Of course you don't need to have it this strong but it is available should you desire this."
Thanks for your help guys, will take a look at your recommendations and links!