Thanks for the reply, it does indeed make it a lot more attractive.

The main issue I have with B2 is that I'll be using some client where the API transaction costs are a complete unknown, at least to me. I have no idea how many API calls of the various sorts the different clients will use, and how they scale with my data.

I have a almost two million files, if a client uses one or two B or C API calls per file when processing the backup set, then that's 5-10 bucks right there.