Burn time?
I used them for OUTDOOR paintball... but I used the large ones, wasn't very impressed. There was almost no wind and it provided no cover. It does burn for a long time, but only a small amount of smoke comes out. Not thick nor dense enough to provide a smoke shield. Was more of a distraction then cover. They are pretty cheap, so give em a try and see what you think. Probably work better indoors or enclosed areas, maybe forest?