Content download time relatively high

[pmeenan]

Chrome, Firefox, Edge and IE on Windows 10 and Safari 9 all support HTTP/2. Safari 8, IE 10, Chrome and Firefox support SPDY though it is deprecated and being phased out.

Google, Twitter and Facebook all have it deployed at scale and have been running some flavor of it through development and yes, it is very ready on the client side.

Server support is a lot spottier as none of the major web servers support HTTP/2 natively (or if they do it is very recent and probably not very shaken out yet). Usually you'll deploy it as a reverse proxy in front of the web server. The best implementation I'm aware of currently is h2o: https://h2o.examp1e.net/