Having gone from electric to nitro heli's to planks, if I was to do it again, I would NOT get a trainer plank, I'd rather go for a good "2nd plane" like a Great Planes Revolver (the larger one), or a Hangar 9 Pulse 60 (or 125) - a DLE20 in either of them would be my choice (re flight times, simplicity, cost of running and POWER!!!!! - lol).
I would still have a few buddy box sessions till your comfortable - but that would only be to get the feel of a plane as they do feel different re the way they fly, and get you to the point your happy landing.
Others may disagree, but that is just how I felt after only one flight of my trainer, and that feeling of "you've just wasted money dopey" just sucked!