Well. That depends :) I don't develop in Emacs and use it solely for hosting Magit, in a separate window. So it's kind of a GUI I guess; more so than a CLI anyway.

> It's Achilles' heel is speed, though -- too damn slow. (Last time I tried it, anyway, which was a while ago.)

Don't remember a single of case of it feeling too slow in the last few years, whether on linux/mac... (maybe it just got better over time though)