I think it actually turned out to be 10 folders including sub-folders within a share... No. The documentation says it is 10 shares with any number of subfolder

I think it actually turned out to be 10 folders including sub-folders within a share... No. The documentation says it is 10 shares with any number of subfolders and that is also my experience - when the Pro trial expired, I could sync 10 shares with a large number of subfolders without any problems. Of course, changing the number of shares from unlimited to 10 was a bait and switch move, and a scam because their website said that they wouldn't remove any functionality from the free version. Also, it's very weird that they switched to a subscription model. You bring most of the infrastructure (bandwidth & disk space) and they bring mostly software (and some infrastructure). Why not just let people buy the software?!?