This could be useful for reclaiming space when your disk is almost full, but $9.99 a month for a tool the average person isn't going to need very often seems a bit much.

It’s not really intended to be a recurring $9.99/mo. It’s $9.99, and that gives you a month of usage. But the expectation is you use it once or twice, then you’re done for a long time. But apparently they also offer an auto-renew subscription for that same price, which seems like a strange choice.