Judging by the code, it seems safe to deref a sub from within a regular sub handler. Is it really so?

Not sure if it’s fine but certainly You can use reg-sub-raw and subscribe all you want from the sub

Yeah, I know. But it creates a lot of unnecessary noise when the handler itself becomes (fn [x _] x).

Is there an accepted way to gather timing statistics for different actions in a re-frame application? Say I've got a user interaction that kicks off a handler chain that includes async IO, and I want to measure the time until completion from the users perspective.

re-frame 10x?