I've seen this "herding" effect on forums with previous cars before. Everyone was going crazy about tune X and tune Y completely changing their cars and what not. I tried a lot of them back then, and most of them were really not impressive or plain sucked.
For the M3 I can imagine the gains with a full exhaust for example, but with an otherwise stock car, or just mufflers, 91 octane, and stock air intake, it's hard to imagine having the car completely transformed with just a tune. Small improvements and tweaks here and there I can understand, but to the level of some reviews I've been reading lately it's hard to believe.
2015 M3 6MT | Yas Marina Blue, CF Roof, Cloth | Adaptive M Susp, 437M 19" Silver | Stripper
2013 X5 xDrive50i | Carbon Black | M Sport + M Perf, 333M | Loaded