It's actually both. When I started it was just B2C but as it grew new opportunities opened up.

>Why is it a one off purchase instead of a subscription?

I, personally, hate having to subscribe to something if I don't feel I benefit from it all of the time. Netflix fine, something I use occasionally, not so much. The product is low cost enough, and changes enough over time that customers come back and buy the product again (I appreciate this is a little unusual). I was always trying to build a pricing model that I would use, no tie in, people respect that and are MUCH more likely to pay for it (in this case).