Limitation on

I’m looking for the limitation of
is it complement free?
How many users ?
and what about the quality of the meeting (I’m in France)

yes, there is no registration at (the actual URL of the service)

The hard limit is 75 but in practice you will often see problems before that, 25 if the computer is not performant (the UI is somewhat heavy by default), and less if your bandwidth is limited of you try to connect to a server in heavy use. It’s a free service and there is no quality warranty.
If this is the case you can try to search for a server at (linking to other servers using the same open source software but with different providers)

it can depend on many parameters see above. Try preferably with Chrome(ium) or the Electron application (based on Chrome engine) here