I've only used one roll (120), shot at 200 and developed commercially.
Grain wasn't too bad, but no different really from other cheaper films.
Where it (allegedly) comes into its own is when you use the specific developers - there is a low speed and a high speed developer.
Personally, I find the cost of the film to high compared to the benefits it gives to me, but I can see the appeal of the versatility - you can rate it from 100 to 3200 or higher depending on developer and time.