At least they documented how to use WebDAV. You could prepare for support try by using that page.
Supporting third party software can probably get difficult, but it may go deeper. For example, on idea:
Jottacloud doesn’t officially support third-party software. See here, here and here. You can read more.
Admittedly they tolerate us fairly well, but break us sometimes as they change the undocumented API.
I don’t know the pricing of all vendors, but sometimes they may hope you’ll pay but not use very much.
Some vendors also throttle heavy users. What’s a good deal for you may be a bad deal for the vendor.