Depends on what you are looking for. As you sais the car is quick as delivered. I had a specific goal, a bit quicker than stock & maintain a good IAT in the Carolina summer. Went with JB4 because it was flexible & had very good customer service. Got an addition bennie down the road when they developed 335is specific maps for the car.
To maintain a good IAT I installed an ETS 5” FMIC which had worked very well. That was it for power mods. I Have a DCT so I blocked out the kick down switch for full control in M/S mode. Car has run a best of 12.5/114 at Rockingham last year.
Now for the downside. They can beat you up big time on your warranty for any tune including the JB4. The JB4 has a pass through map that goes back to stock for light service like oil changes but for major warranty work you need to remove it, about 1/2 hours work about you have done an install & know what you are doing.
The FMIC is pretty much an unknown factor with some reports it’s a problem & others that its not. Will have a better idea on about the FMIC on Wednesday, am going in for oil, brakes, wipers & a slight coolant leak that may trip the warranty alarm. If they will not look at the leak will take it to an Indy for that issue.
You modify a car you really need to be prepared to pay the bill out of your own pocket for some work.