For bigger groups it is actually quite good. Its also a more lightweight experience as opposed to Discord with all the chat ect. functionality. And I have found it to be more ressourceful than Discord.

That being said nowadays I use Discord 95% of the time.

I don't know if it's actively maintained anymore because it's been a while since I played, but there was a mod for Arma 2 that simulated real radio physics and depended on Teamspeak.

Still maintained: https://github.com/IDI-Systems/acre2

It looks like progress is being made on Mumble support: https://github.com/IDI-Systems/acre2/pull/980