Tweaks - more
The wireless radio temperature tracking page is kind of interesting. Since increasing transmit power makes the radio run hotter, which will decrease its lifespan, this graph attempts to let you make an informed decision. I didn't mess with transmit power at all to test this. As I mentioned in the past, I've never had good luck with boosting transmit power on other routers and don't expect that to be any different in this case.
Wireless radio temperature history for transmit power tuning
I did run an unofficial wireless test on the default transmit setting with LAN Speed Test just to see how it fared against my NETGEAR WNDR4500. I only tested 5 GHz, but I saw about a 10-20% better throughput, something confirmed in the router charts.
Merlin firmware also adds an OpenVPN client and server to the firmware to add more secure VPN options (OpenVPN uses SSH) than the stock PPTP-based VPN server.
OpenVPN client and server options
SSH is also added as a login option for secure command-line management of the router.
JFFS partition and SSH options
The screenshot above also shows a persistent JFFS (Journaling Flash File System) partition option to support configurable scripts.
The last notable feature addition is the option to use short names for shared folders vs. disk name-folder name convention used in ASUS' stock firmware
While open source based firmware like DD-WRT and Tomato are valuable in their own right, ASUSWRT-Merlin adds a lot of value to the ASUS' stock firmware. Eric's main focus on bug-fixing provides improved stability. And his selective approach to feature addition doesn't put that improved stability at risk by possibly introducing new bugs along with features.
The dirty little secret of alternative firmware is that the open source drivers it must use aren't always the best. This is particularly true of wireless drivers, where chip manufacturers work closely with their customers to squash bugs and tweak performance. By using ASUS' own code as the ASUSWRT-Merlin base, Eric is able to provide value to both users and to ASUS, which is a win-win.
While other alternative distros like DD-WRT and Tomato add a wealth of features, they usually introduce problems of their own along with potentially lower performance. Eric Sauvageau's ASUSWRT-Merlin firmware provides improved reliability and a few carefully-chosen new features, while not putting performance at risk. It's a minimalist, first-do-no-harm approach that is very refreshing.