I would be happy with an explanation of "none of our service is guaranteed, but if we don't manage to give you your chosen GPU more than 80 percent of the time, you are free to cancel, and we will refund your final months subscription payment".
Since the subscription is monthly with no commitment, I think the viewpoint is probably something like "if it's not meeting your needs then unsubscribe." A refund of $10 is not going to be economically meaningful to folks who want to subscribe to this service. "Chosen GPU more than 80% of the time" sounds nice but it opens you up to adverse selection. They aren't looking for customers who want to pay ten bucks a month to rent 80% of a high performance GPU. That's not nearly enough money for that kind of commitment.
They have a product with guarantees, but the market price for that is literally 100 times more than this one. If you want a certainty of getting the calculation unit of your choice and not getting kicked off of it, then that's not going to cost $10/month.
