A counterweight will equalize the forths in both directions because it overcomes the gravity in one direction. However, you'll still have inertia with an actual counterweight. Gas springs don't.
In the end, hard to believe a small machine like that really needs a counterweight. The head just isn't that heavy.
I'm pretty sure Hoss experimented with a counterweight on his X2. You should ask him if it was worth the trouble.
Best,
BW
Try G-Wizard Machinist's Calculator for free:
http://www.cnccookbook.com/CCGWizard.html