Started october 2014 at th4 (stopped playing for a while after initial download) currently level 101 at Th9 I am 80% maxed on troops and defense with BK10/AQ13 & 75% legos rest skulls. I only gem barracks to raid. I did gem some troops at th7 though maybe 4 or 5 of them. Have not gemmed anything but barracks, spell factories, heros and drills/collectors/mines since. Best use of gems in my opinion. I like to play a lot though like 4 hours at a time.

