That's amazing........ That Tower info page is the first one I've ever seen them do that had important information omitted. They usually make a point of stating everything, even the most obvious. Nowhere on that page is there a clear statement of what the 3 channels do.

That said, very often 3 channels are for rudder, elevator and motor.... but not always.

Ailerons are a good idea, and good to have on a trainer. If for no other reason than the possible confusion for a beginner when his first airplane is rigged with the rudder on the aileron stick.... or not.... see, it's even confusing to describe it.

That airplane looks like a good price, but I'd suggest that you find a 4 channel trainer. If you progress at all in your learning, you will want more than it's rudder/elevator very quickly. And rudder/elevator planes are flown differently than other planes.