They are pretty much interchangeable among brands, however, not among themselves.

For instance, don't put a Futaba and an Airtronics on the ailerons (one on each side). If you are doing something like a servo per side on ailerons, elevators, flaps, or any other control surface that has a servo on each side, keep the servos the same manufacturer and type.

For instance, if you use an Airtronics 94102Z (for example) on one side, use the 94102Z on the other side. That will keep speed, torque, resolution, and so on, the same on both sides. This is not peculiar with Aitronics, by the way, it applies to any of them - Futaba, Hitec, JR, Spektrum, and so on.

However, since the basic standard servos from most manufacturers run about $10.00 each, you can easily buy them in pairs.

Also, keep in mind that, unless you really need a high end servo, most of the standard, basic servos will work just fine.

Oh, you can do this too: (again, example only) two Airtronics on the Ailerons, two Futabas on the Elevator, and two JR/Spektrums on the flaps. Just keep them the same on each of the control surfaces, but you can mix them on the airframe. I often use a low torque micro servo on the throttle. It saves space, and when set up properly, without end point binding, they don't need much torque to open and close the throttle.

CGr.