Merlin Firmware for ASUS Routers is great. He is a developer and gets ASUS Routers before they are available to the public. A lot of the improvements he codes are used by ASUS in their firmware. I've been using Merlin for a few years now on different routers and never had any issues.
You should give it a go, and if you don't like it, just flash back to stock ASUS.