I played CTC in a pure DE list at the BAO this weekend. I ran into only 1 mech heavy list and only 1 Toughness heavy list, the rest were balanced.
I used heat lances, and they were really only relevant to killing tanks in 1 game, in other games positioning mattered far more than one they shot. In one other game they did affect a knight's positioning though.
In retrospect, I would likely save the points and stick with cannons. The reasoning being, they simply don't come into play enough to merit spending points on one way or the other.