I have both a Zero and a Mustang, fantastic planes!
You need to do a couple of things to make the Zero fly well:
Set the COG as per the build manual. Mine is set at 60mm from the front of the wing.
Move the battery pack down onto the wing. I cut the battery tray out completely. This might mean having to move the aileron servo back, which I did.
Set the elevator so that the bottom of it is in line with the bottom of the tailplane. (trimmed down slightly in other words)
It will then fly very well. My Zero is the best plane I have ever had, it flies like a dream.
Here is a video to show how well it flies with the above mods:
http://www.silentflightonline.com/Si...mages/1208.wmv