@e-maddin - the Gardena manual states the 1278-20 is 24 V A/C so it should be compatible with Rachio.
I don’t have Gardena valves, so I can’t test to be sure and I don’t work for Rachio, so I don’t know if they have tested out those specific valves. The main issue would be pulling too much current, which mainly happens on pump start relays - I wouldn’t expect those valves to pull too much current.