mosh is basically a proof of concept as a college project - it is missing Unicode and ssh-agent forwarding which may be significant for some.
Otherwise it works decently well for what it does. For many screen and normal ssh will do the job.
Re: Unicode, please see https://news.ycombinator.com/item?id=28151652. (Mosh really just uses your C library for knowing the width of characters -- if the server's and client's libc support a character, Mosh will too. Unfortunately Apple in particular has historically been not super-great about keeping theirs up-to-date once Unicode went to an annual release cycle. screen and tmux have similar issues and basically ship their own Unicode tables, which has its own problems.)
For ssh-agent forwarding, most people are using https://github.com/StanfordSNR/guardian-agent which is more secure than traditional agent forwarding, and works with SSH or Mosh.