I have had trees from them.
Just let them grow the first year, avoid them fruiting to put the energy back into the roots rather than the fruits. If you can.
They are young trees, hence the price. You could transfer them later, into the ground. It depends on just how big the pot is. A huge one will keep them for a couple of years. But they are not meant to be tiny and will grow to big standard trees eventually.
As for pruning, that is highly debated but the fact is that growers prune to produce huge volumes. You wont need that quantity but you will eventually want to cut large branches which grow in places you do not want them and that is what I do with my established fruit trees. Chop them off when they grow where I do not want them and I still get loads of fruit.
Keep them watered though especially if there is a dry spell. A bit of feed wont hurt.