Is there any disadvantage of the RH-20 back? I assume 120 film can be used, is this correct?

Correct. When using 120 film with the RH-20, don't forget to stop taking pictures after "10". Then it's a bit tedious winding on through until you can reset. Also there may be issues with frame spacing; Graflex roll film backs, in my experience, are highly variable in this regard. Best way to find out is to run a roll of 120 through your RH-20 to see what if any eccentricities emerge.

Okay this is nit picking, but in better film backs, 120s were designed to compensate for the paper backing while the 220 didn't. Certain cameras even had a way to change the position of the pressure plate so it could take either one.

While RH10s and 20s were better than the Graphic 23s, these were still no fine piece of workmanship. I'm throwing this out so that in case you notice a drop in sharpness at wide open with 1120 and not 220, you'll know why.

Good advice, Les. But would you agree that it's best to avoid shooting wide open if at all possible?

Let's play devil's advocate then. Graflex backs are relatively inexpensive but I'd rather get a good modern back even if it costs more if it will avoid problems. I;ve seen used Wista backs for under $300. What say ye?