Thanks!! The Loadster Fuel option is just that, where you buy a bunch of "fuel" (credits) and use it whenever you need to run tests. Each unit of fuel is enough to run 1 virtual user for 1 hour and it never expires.
Loadster's revenue split is something like 70/30 between MRR and Fuel. As the founder, of course, I love MRR, but many customers are like you and load testing is an occasional activity where it wouldn't make sense to have a recurring commitment.
I do always wonder how much friction it causes having two separate pricing models... pricing is hard.