I personally dislike the subscription idea because I generally only use the tool every couple months to find a trip, and then I'm dormant for weeks/months while I work. So subscribing for a year to only use it for a couple times seems a bit odd. But that's my personal usage. Something like x USD per 1000 credits IMHO makes more sense? That said it's obviously totally up to cow and I'm down with whatever, if that means more donations then that!

I have no idea, but are there legal concerns with making the tool paid-only as far as "you're making a profit off using AC IT resources" or the sorts?