Depends on the size tree you plan on putting in them. What are they in currently?

They aren't too big, I'm just wondering if this will give them the correct growing environment for training and helping them to grow quickly.

Pots are made of inert material, and as long as they have good sized drain holes and are otherwise suited to the growing habits of the trees in them (e.g. maple roots grow laterally and so a wide pot vs deep is in order), they should be ok. However, you don't seem to appreciate that different size root balls must have the correct size of pot, whether rectangular, oval or cascade, and while the pots may be great for training in a general sense, unless they're the right size for your trees, they won't be any good. Plastic is not a problem except that in very cold climates they can tend to crack over the winter, so that could be a consideration depending on the climate, type of plastic and whatever wintering techniques you use (burying, garaging, etc.).