I have used only on GT5 Prolouge Spec III.
The FFB parameters required the highest settings for it to feel right for me. I have used the Logitech Driving Force Pro. The GT wheel is very similar, but the FFB settings on the GT are lower compared to Pro. The FFB seemed notchier on the GT wheel, but nothing that was too distracting.
I constructed a folding stand to accommodate the wheel and it's FFB. Using a table didn't work well for me as the height wasn't right. Not everyone can construct a stand, but I recommend making or budgeting for one. Unfortunately, an FFB wheel is no good by itself unless you have a stand that works.
I am sure the G25 is better, but $100+ dollars better I am not so sure. Not for me at least. I can buy real performance parts for my car for that price.
The real-time vehicle adjustments are nice. I didn't think I'd use it, but I ended up liking that feature.
Overall, a must have for Gran Turismo and other sim. racers.