Just to add, I have attached a picture of the servo installation from my world models Frontier 40 manual. Although this is not the same model, the installation is similar for most types of trainers. As you can see the installation uses one servo that is connected to both ailerons through the use of torque arms. This is more than sufficient for most trainers such as the NEXTStar 46 as you do not need the extra power/torque and rigidity provided by two servos, in fact there are even some sports models such as the Word Models Mach II that use this set up. The only reason a beginner would need two servos in a trainer such as the NEXTStar is if one wants to experiment with flaperons (this is when the ailerons work as flaps and ailerons at the same time). You will never need flaps in a trainer, but some people like to experiment. When it comes to the extra rigidty and power of two servoes, as a beginner you will never be able to tell the difference between a one servo or two servo set up. I doubt that any body besides the most advanced pilots would be able to tell the difference in set up between a one and two servo set up in a trainer.

I am not to sure what type of radio the RTF version of the NEXTStar comes with, but if you want to experiment with flaperons you will need at least a 5 channel radio with flaperon mixing built in (their used to be some after market devices that could be fitted to the plane that could do the mixing but I am not to sure if they are still available).

Hope this helps,

Cheers
Pups