I've used the Polar ND filter for several months and I have never counterbalanced it. It seems to work fine and I've yet to burn out a motor. I've done this on all 4 of my H3-3Ds. However, I've noticed if I make aggressive moves, sometimes the gimbal will "drop", meaning it'll tilt straight down and re-center itself. I'm pretty sure that's due to the additional weight of the filter because I tried to replicate it w/o the filter, but it won't do it. It's kind of alarming when it happens because I'm looking through my goggles and it appears as if all hell is breaking loose, but since I know what's happening, I just wait for it to reset and that's usually a few seconds.
Btw, not saying NOT counterbalancing is the way to go, just sharing my experiences. My reasons to not counterbalance were because I didn't want to add more weight and I just didn't want to go through the trouble.
Counterbalancing or not counterbalancing....if it works for you, then you're doing fine and that's all that matters, right?