As was mentioned by others, don’t bother with a charger for a PHEV, especially since you pay out of pocket for it.
It would only make sense if your next lease is an EV, but in that case, you should just wait until then and get the free charger through MB.
Energy prices depend on your location, what’s cheapest for one guy might not be the best choice for you.
I don’t know what car you got, but take your battery size and divide it by 2.3, that gives you a rough estimate on how long you’d charge on the granny charger. You keep a PHEV plugged in over night, a granny charger will charge it to full in 5-7 hours (unless it’s like one of these new long range PHEVs with 120+ miles range).
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.