I use the Sunrise Internet Box (Sagemcom) without any problems. Set up in 3 minutes. I am very satisfied.

Yes, that's what I have in use and everything works well so far. However, a Fritz!Box is needed to operate a mesh network.

I'm sorry, I don't know. I use it together with a Fritz!Box. According to the description, the repeater is also compatible with other routers. I can't say whether the mesh function can then be used. It would be best to ask AVM.