Keep in mind that (model) scale planes are harder to fly than full scale ones. Take a 1/4 scale cub. The overall size of the plane is 1/4 the size of the full scale, but the controll surfaces are actually 1/16th the AREA of the full scale ones. If you follow this, you'll see that the scale plane has less controll surface relative to it's overall size, and therefore is less stable. Also, a Cub is a plane that requires you to fly it with ruder all the time, and to fly it from the moment it starts to taxi, untill the wheels stop. A trainer is designed to let you learn how to fly RC, as it takes off and lands slow, is stable in the air and is very forgiving. That's what you want in a plane to learn on. Plus, by the time you've soloed and start flying on your own, that little trainer will look like you kicked it up and down the flightline with baseball spikes, due to all of the repairs you'll likely make to it as you learn. Do you want to have your Cub looking like that?

My advice is for you to buy the Cub, and buy a trainer too. Learn to fly the trainer until you're good at all of the skills needed to fly the Cub. Since you will have a specific goal in mind, you and your instructor can work on the differient skills you'll need to fly the Cub well, like coordinated turns, slow flight, etc. You'll enjoy that Cub much more in the air than in the trash bin.