I think it's time to call it quits on user-agent sniffing. http://blogs.windows.com/msedgedev/2015/06/17/building-a-more-interoperable-web-with-microsoft-edge/
Was never a good idea, and will only become worse as an idea going forward. Test for features on the client, don't guess on the server.
Why? Let's look at what Microsoft needed to do to get the new rendering engine to work on most sites. This is the new UA string:Mozilla/5.0 (Windows NT 10.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.135 Safari/537.36 Edge/12.10136
See how many different rendering engines you can count.