When we renovated and added a two story porch we also had spray foam added in the entire attic. Company removed all the old vermiculite in the floor of the attic, and then sprayed open cell foam across the underside of the entire roof deck. Very effective, and no issues at all with off-gassing, smells, etc. Attic is now only a few degrees warmer than the 2nd floor rooms under it, even when temps hit up 90's. The foam we used was Icynene, which had a little better R value than other choices, and it is supposed to be more environmentally friendly.
We did not cover the foam because there are no attic windows (therefore no UV) and we did not plan to have anything up there other than the A/C unit. If we had wanted to use the attic for storage space we were told we must either cover the foam (sheetrock, etc.) or have it sprayed with a flame retardant.