Absolutely the best server manager for AC, hands down (and I have tried them all in my time as a league admin). Trivial to install, immensely powerful and easy to use, for everything from quick one off races to complete championships with fully configurable race weekends.
The devs are responsive, both here, on GitHub and in their Discord. Bugs are fixed promptly, new features are being constantly added, and they are open to merging code features from contributors (I wrote the Discord integration, which they were very encouraging and helpful with).
Please ignore any 1 star ratings from people who couldn't install or run it. If you can read a short paragraph of instructions, you can run this.
At the moment is isn't possible to force people to use any app (including Sol) through the manager. This is because the server has no knowledge of whether or not a client is running Sol (or any other app), so unfortunately we can't do anything about it. Sorry for that, but I hope this answers your question!
Thanks