I almost use rr every day, along with a gdb frontend: cgdb.

rr record /tmp/Debug/bin/llvm-mc a.s && rr replay -d cgdb

I've have success story with some bugs only reproducible with LTO. Without rr it would be a significant challenge.

It would be nice if Linux kernel could be debugged with rr. Does anyone have success with kernel under rr+qemu ? :)