Yinzer - price difference was for the product, not the labor. On second thought, labor may have been a touch less because for the same effort you get more R-value. I don't recall how we priced the job. I had it done about 5 years ago. As I recall, you have to do multiple sprays over the same area with open cell and just one with closed (assuming 2X4). I had 2X6 and had them run a second spray anyway (it is a western-facing wall in Chicago...cold and hot!)
I would watch out for the facing on the studs. They need to prep that (i.e. keep the foam from getting onto them.) If they do not prep properly, they will spend a ton of time trying to get the facing of the studs clean and ready for the sheathing. That could be a problem. The other problem was containing the foam if the wind picks up. Ensure they put up a tarp on stuff below and anything you don't want foam permanently attached to. Neighbors are weird like that (not wanting your foam on their new exterior lamps, lawnchairs, etc. ) (Joking there)
My recollection is that I went with Dow but there are plenty of brands. I picked Dow because the pricing was similar across all brands and I knew Dow was purple, so I could audit/confirm I was getting what I ordered (you will understand when they show up with the product. You ever see an independent gas station get fuel delivered? It could be any brand just the cheapest at the tank farm. Same theory.)
NSXRguy, your PM is full. I could not respond.