FireDragon from Garuda.

Oh it has dual partitions for kernel which makes it easy to recover from an error.

https://www.reddit.com/r/openwrt/comments/1fgta78/guide_to_installing_openwrt_on_the_20_linksys/

I'd argue the Linksys LN1301 (mx4300) already suites this purpose better than the "one". If you can find it for the same price or less I'd grab one. Comes with 2GB ram, 1 GB flash and was being sold cheap ($25) from woot and amazon because the deal the hardware was intended for fell through. Does mesh, has usb 3.0 etc.

Openwrt snapshots are available but it's not yet in the mainline source. I replaced a $90 asus router with one and have been very pleased.