Mike,
I've used it in the past, and liked it real well. The consistancy is good and shrinkage isn't bad. Yes, you can sand it in 30 to 40 minutes after application. My problem is that the local auto supply stores don't stock it so I use the 3M Laquer Red (If you want something that really dries fast, try the 3M Laquer Green. If you are going to putty a 2 inch seam, it will be hardened before you are finished and sandable in 15 minutes)
If you have a source for the blue, go for it.