Mono is pretty well established, see Mono (software) - Wikipedia. Back when I did Java servlet development many years ago, I did try out Mono on Linux. I didn't find much use for it but I did think it was neat, as kind of a novelty. I've never tried MonoDevelop.
Personally, if I had a MacOS device and no suitable Windows device available for .Net development, I think I would use a virtual machine on MacOS to run Windows with Visual Studio. I think you get the most benefit out of .Net when used in combination with Visual Studio.