@jamesahy. I just saw this post and I apologize for not getting back sooner. When I visited the Remus headquarters we actually installed a couple of these on a Mini F56 and a BMW 320i. We only did the install on the Mini for training purposes but we did dyno the 320 and it was quite impressive. They are all tested on the European models and the octane is higher so the gains may be a bit higher for the European cars compared to the US but only minimal.
The unit allows you to drive in different modes. Most will drive it in sport I am assuming but it alows you to control the modes by using the external buttons on the box. We were able to increase the HP on the BMW by 60 HP using the Powerizer. The settings will not be that high when they are sold but it goes to show how much the engines are detuned when sold. The tech had to use software to change the settings on the unit to get the 60 HP gain and that is not what the end buyer will see but it does show the capabilities of the unit.
The piggyback concept is nice as it stays within the parameters set by the factory without exceeding them. If they are exceeded the CEL will come on and you can adjust the box down to get within the mapping parameters. There is no flashing involved and can also be removed with no trace that it was ever installed.
We do recommend having an experienced shop do the install and follow the directions to a T as any wrong connection will trigger codes so you must adhere to the install instructions very carefully. The results are impressive for the cost and when combined with the Remus Responder it is like driving an entirely different car. Please feel free to contact me with any additional questions should you wish. Talk to you soon.