I like the JJs now. Its hard to hit anything on the way up, but on the way down its more or less the same, which means that there is a decent window where you can see your opponent poping up but he can't return fire efficiently. It turns pop-tarting into more of a strategic maneuver than an actual method of combat.
My only complaint is the amount of heat buildup vs height/distance gained. Today I was on Inferno and felt very smart bringing a mech with JJs until the fighting started on higher ground in front of me and I couldn't jump high enough to get up and over the wall before taking the heat into the red and almost shutting down. Though that might just be Inferno.