The sticky thread in this sub forum has a video by Cope that covers exactly this. Low band apply in 1st gives an extra holding measure so the sprag isn't the only part working to engage 1st gear. Bolt-in sprag is a good safety measure but alone won't save the trans. Billet front drum is what will save you from an explosion from over revving internals at the end of the day.
Cope also makes the point that TH400s also explode, not sure if Powerglides work in a similar way but 400s explode at the big end instead of at the starting line. IMO if my transmission is going to explode I'd rather have it happen when the car is first accelerating than when it's going 120+ mph...
Regardless of all this talk about explosions I have no reservations building up the BB 727 I have with these 3 upgrades to go behind a 600-700hp 440 in a street/strip car.