The problem with them lies in the fact that they aren't meant to kill. They are tactical nades. You can tag somebody and run off and heal, then they will still be being burned. Then you can tickle them and they die. If you tag all three enemies (in trials of course) then you can run back, get a res, and then one shot each one. They put guardians out of commission for 14 seconds. That's a long time in a shooter like Destiny.