The only negative of spi for me is cold weather... you must keep it above a certain temp for 24hrs. Otherwise it's all I'll use once I'm out of the leaded ppg I stockpiled

As far as doing 2k primer or putty directly over the non sanding ppg, you still end up sanding into it and ruining a lot of sand paper. You can get epoxy for half the price that will do the same thing.