First of all, the 9402's are a bit heavier than most high-torque servos. The reason why they aren't so popular in helis is because the metal gears tend to develop slop very quickly unlike similar others that have nylon gears.

On planks, unless we're talking about a super high speed plane such as a Q500 or so, it doesn't really matter (at least for most of us) a .25mm play in the rudder or ailerons ... in a ccpm heli that would be the difference between perfectly vertical ascent to a crooked ascent.

basically, if you already have them, use them. If you're planning on purchasing them you might as well get the 9206's instead.