One mans advice- 

When I am playing with some electronic tempo-master.. I do my best to recieve master clock from that device. 

When I am playing to a Drummer.. even if he or she is playing to a click, I use a tap tempo on my board, and during almost any lull in the music I re-tap to ensure accuracy. This ensures my effects are on tempo if the drummer is perfect.. as well as ensuring I am on tempo if they are NOT 🙂

I would never rely on co-inciding matched bps to actually be in sync, even with rackmounted equipment… much less with a stompbox. You might get lucky some times.. but eventually you will blow it.

my 2cent