Sounds like Lifetime Pro is $40, up from $30 until December 10.
https://appraven.net/app/212961449
(Yearly is more expensive.)

Sounds like the freemium is partly about the number of (concurrent) sessions, though projects are unlimited. The free version also has only one theme (this generic “Dark theme” we get from vibecoded projects).

Ah, digging a bit more…
The Pro version has auto-detect key & tempo (the kind of thing which requires testing).
While the free version uses a sync mechanism (Dropbox, iCloud, etc.), backups are a Pro feature.
There’s also a tab in preferences for “A…” with a big “Pro Writes” badge… which sounds like it’s about API. (The help button is greyed out in the free version).

Licenses are individual:
“A license is for one user and can be used on your machines. If multiple people are using SessionDock, each person should have their own license.”

So, for collaboration, it means multiple licenses.

Glad that it doesn’t require an account and the app isn’t sending data.

tbh, strikes me as a vibecoded* app in the “scratch your own itch” category. While it tackles “a problem every producer knows”, it’s not clear that the approach hits the sweet spot for all “producers”. We’ve yet to find a proper solution for those common use cases.
One tester is thanked, so there must have been a testing period.

*(Not that I find anything wrong with those, as I’ve been vibecoding several projects for the past two years.)