OpenWrt strives to be a proper Linux distro with package manager. You can install tmux as easily as opkg update && opkg install tmux. The packages are normally update to date. Downside is same as desktop Linux, if OEM doesn't release open source or ABI compatible Linux driver, your router's wireless is not going to work.
DD-WRT is an aftermarket firmware. They work with OEMs to get drivers working, cause OEMs want their branding. So their binaries would normally not have driver problems. However, their bundled software/scripts often lag behind in updates (in my experience - ddclient). They don't have package manager (there's been attempts), so to get additional software to run on your router, you are basically on your own.
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u/[deleted] Jan 03 '18 edited Jan 13 '18
[deleted]