I am using it, and I like it, very fast and easy to maintain. Never used wordpress so I cannot compare the two products What would you like to know about Grav? Can you be more specific?
Once they release the wysiwyg I suppose. Have they? I haven't followed their development that much. It's not that easy to convince client on markdown (tho I've gotten a few falling in love with it.) A file-base system can be quite slow too if your site has lots of pages like 10k+. Other than that Grav (and Kirby) had been a joy to work with.