Personally, I use 3 coming from 2 different purchases and different brand (they are identical and compatible !!): 3 receivers and 1 transmitter for my config (I have one transmitter rabe).
To be clear, this system does is trigger (s) flash (es) in sync via the contact X dematerialized here: no exposure data! Flash units must be set manually beforehand. Exactly what I wanted and what is better: simpler and faster.
Quick Tip: To set your manual flash, nothing like a hand cell / digital flash meter SEKONIC L308S: a gem that has remained with me from the time I was using a Canon F1 silver mechanical (manual and all)! !! so it was a good perennial purchase!