I have gotten only one leg engram at the end of strike roll. I have gotten a few dozen from the mobs on the way. I average 1-2 blues per run on the mobs and 1-2 from end roll. In most cases it only saves like 5 min tops skipping mobs and it takes 15 (10 if rushing) to do a strike with a decent group. So if I don't kill mobs I get 1-2 engrams for 10 min or if I do I get 3-4 in 15 min.