The tutorials here cover the timers and interrupts, but separately. In the code library, the frequency counter example has timer interrupts.

A timer interrupt service routine is generally simple: reset the timer, do something (often just setting a flag) then leave. It all depends on what you need to do. I use them for timing message broadcasts, parsing messages, blinking a heartbeat LED, ... lots of things.

I'm curious why you're comparing two different things (timer interrupts and state machines). Kinda like apples and oranges, they're different but both are good.

Dennis