I've used "Great Stuff". Here's my thoughts.
It has to be sprayed upside down. That sucks, 90% of the uses of it would benefit tremendously with the can upright. Say, filling in the gap of your sill plate on top of your foundation, I had to get a ladder, climb up, reach out with one hand hold the can upside down, with the other direct the straw where I wanted the stuff to go, while moving both together on the ladder spray it at the joint for oh... 16". At which point, because the can has to be upside down I hit the floor joist and needed to stop. Climb down the ladder, move it over 16", climb back up, put it between the next floor joists, rinse, and repeat. I can do about 8 of them before I need to take a break for a day so pissed off about it having to be upside down. Or, I love the "fill in the gaps around plumbing". You know how hard it is, to hold the can upside down under a sink, trying to keep it high enough, and with your other hand steering the straw where the plumbing penetrates the wall and try to keep the can in a postion it's out of the way of the sink, the drain, the drain plug, the hoses, the valves, and reach to the back wall. I had to have my wife hold my feet down while I stretched as far as I could trying to do it and threw out my back trying to "fill in the gaps around plumbing penetrations".
You don't want any of it in view. Having so much difficulty trying to do my sill plate on top of my foundation I went around my house and sealed the gap with it between my foundation and shingles of my house. Well, that was all fine and good until the stuff turned flourescent orange in one year and my house looked like it was invaded by a flourescent mold. So, I had to go out with a razor and cut all the stuff out.
It's a one time use product. About 2 out of 3 times if there's any left, it's unuseable even when cleaning the straw or cutting it back. That, or it's performance and application seriously degrades if you try to use it a second time. Make sure, when you buy it at the store it has the straw attached. More than once I've come home to find I hadn't noticed some fool had taken the straw off it in an attempt to use theirs a second time. I then, have to go to the store and take a straw off another and have it happen to someone else.
The materials itself costs about 20 percent or more over regular insulation and it MUST be done by a licensed contractor. The stuff is EXTREMELY flammable, last summer a construction crew was insulating and sealing a house. A construction worker was going around with Great Stuff sealing gaps while smoking, and his cigarette lit the stuff on fire as he was applying it and the house caught fire. When it dries though, it's self extinguishing. It will not burn unless there's a constant flame on it. You take that flame away, it goes out.
All this, and I have to say I don't think it's going to work. A large can of it will probably fill a 2' high section between 16" framing. You have a 9' wall and you'll need around 4 cans... each at about $6 that's a very expensive project. Also, I've never seen the equipment you can rent for it, only professionals own it and you have to pay them to apply it. You're much better off insulating it yourself. Any reason you're interested in the spray foam for the 2 car garage? I know they used it in a barn for "this old house" because the old barn had so many air leaks, had settled, was not square, and the framing members all over the place it would've been extremely tedious to insulate it and make it air tight. They chose to use the polyurethane foam as it filled all the gaps and odd spacing, and then they cut it off with a knife.
