The Linksys WRT3200ACM has A/B firmware support, but unfortunately that router is starting to get a little outdated. Saved me from a couple bad upgrades, but unfortunately it died on me about 4 months ago. I updated to the Banana Pi BPI-R3, which has been great for my network speed, but was a lot more complicated to set up.
“That’s a sandwich worthy of Dagwood Bumstead!”