We mostly stick to a single master with our code, but this was one case where we branched so we could watch progress via test passing percentage to make sure we were moving fast enough to finish before we got sick of it.

Definitely have been one or two refactors that have been shutdown. We've been lucky to have clients that give us the freedom to retire some technical debt/risk instead of just churning out features. And we're small enough (200 kLoc approx, 6 devs) that full codebase refactors are still doable.