The Microtik RB750gr3 is a very nice router for the money, and plays nicely with OpenWRT, too. However, it comes with very little flash, so it needs an extroot on a MicroSD card. Unfortunately, the stock OpenWRT 22 appears very picky about the card it will work with.
ext4_check_descriptors: Block bitmap for group 0 overlaps superblock EXT4-fs group descriptors corrupted!
I'm clearly not alone in having this problem. e.g. this post on the OpenWRT forum
It turns out that both the suggestions there work. Updating the max clock speed and recompiling OpenWRT worked, but I'd really rather not be maintaining a custom version just for my router. So, whilst an "Amazon Basics 128GB", (C10 U3 A2 speed card) does not work, a genuine "SanDisk Ultra, 32GB" (C10, U1, A2 speed card) does work, for me, with the stock image.
