Keg Connection also has a regulator that goes directly onto the 20oz paintball CO2 tanks. I got one in my last order. IMO, a better option since it won't have the regulator sticking straight up on top of the tank. I would still make sure it's in a place where it won't tip over.
I'm thinking about getting a second 20oz CO2 bottle today, as well as getting both of them filled. I have one 5#, one 2.5# here (on top of the single 20oz), one 2.5# on order (Keg Connection again) and just ordered one of the 20# aluminum tanks posted in the classified section (of HBT)... I plan to use the 20# once it's filled (and ensure the hydro date is good). The 5# will be the primary backup tank. The 2.5# and 20oz bottles will be additional backup tanks as well as for when I take a keg to a gathering/party. It might seem like a lot, but I want to be sure that I'll be able to keep kegs on gas while filling tanks.
You can also go with the adapters if you want to go cheaper. If you have it strapped to a keg, it won't be an issue. If you have it outside the fridge, it could be a problem (getting knocked over)...