It really is usable, and more importantly, it really is FUN - that's why I have the car - FUN.
If you have 600hp, and still plan on using 7" wide rims in the back, yeah, I can see where it's a problem. Add the right tire package, and the car is completely controllable. I don't have quite that much power, but punching it in 2nd, the tires go into a slow spin as the car accelerates. I don't just smoke the tires in an out of control burnout.
There are a few members here who have gotten rides in my car, and a couple who have driven it. I think you will find the consensus is the fun factor is high, and the car can put all the horses to the ground just fine.
I admit that given equal drivers and equal tuning time, my car will not be as good in an autox setting as a 200hp Caterham due to its wider stance, but I bet on a road course, it won't even be close - in my favor.