See the long, tiresome thread in here about OpenWRT metarouter on RB450:THREAD
It is unstable. Reboots, lockups, etc. MT cannot narrow it down and it remains a mystery.
I have never had a problem getting the image built, installed and running, it just won’t run for long and the host hangs/reboots. The 751 may be a little slim on memory, I was using the 450G.
opkg works fine, although you either have to build the packages or find a repository.
It really is a pity as it adds so many possibilities to this little box. I have resorted to adding a cheap Openwrt box on the network to do the things ROS doesn’t.