I keep saying that "rollback" is an overrated feature. And i stand by that in the general case. I've always said that it may help in special cases. Fortunately today I had a special case where #nixos rollback was exactly the thing I needed after finding a regression in the current Linux 6.1 LTS series that broke a router config. I'm grateful it's there, and this has been the second time I can remember when I used it.