Krispy, I've been thinking about getting the same thing. I already have boots with regular felt on them. They're about six years old, and the felt is wearing thin from the many miles they've covered.
I want to buy a replacement pair, but so far i've only seen one type. They've got steel studs that are permanantly set into the felt. You said the ones you've seen have replacable studs? That would be much better than what i've seen.