I gave this mod 5 stars, simply because it deserves it. There is no discernible quality difference between these and ISI karts, it's just they are provided with a variety of cog sets, as is the case with the karts at your local track.
There is a reason all the great drivers started in karts, so if you haven't before, maybe it's time to go back to High School ;)
There is nothing in the consumer market that provides such fidelity... There is nothing that provides me with the spectrum of feeling, all those little details you are only aware of when they are missing than this masterpiece. It scares me how talented ISI must be to get it to feel so real and I feel at least semi qualified to say that as a hobbiest programmer/modder and an ex karter. Nothing more but it gives me a good look behind the scenes.
Huge thanks for those involved with this mod, I'll be still racing it in several years time, I can assure you of that.