Unless you use a common clock signal there is always going to be a drift. Even if you have two metronomes of the same brand, start them at identical times, they will eventually drift out of sync.
The only tempo issue should be whether the factor pedals are slaving properly to a steady MIDI clock, and whether the display is a a reasonably accurate approximation either the received or generated MIDI clock..
I have found the TF and PF to respond to a high degree of accuracy to a single tap tempo switch wired to both pedals, with only a minimal drift after a few minutes. .. Haven't used either with MIDI clock yet.