Although I can't speak about having a catless setup, since my car is otherwise stock aside from the Evolve Tune. I can try to answer some of your questions.
1) I did gain some nice midrange power that increases and pulls to redline.
2) I've really only hit the 8600RPM once or twice. It happens so fast and pulls rather strong.
3) Flashing process is so easy and fast, especially with the updated version of the evolve-R PC software. It probably takes a max of 5min to load the tune onto your car.
4) Incredibly easy to update. Evolve can send you the files just the same, flash the car the same, takes a few minutes.
5) Evolve's customer service is top notch. They have been very accommodating and informative. From them alone, I have learned a lot about how our cars work, how tuning works, how to dyno. They also answer a lot of other non-tuning questions regarding cars.
6) I would highly recommend it. They've done a lot of work on my E46 M3 and it was only natural to point to them for my E90 M3.
Evolve can also update your DME to the latest 231E update.