Carrie, I also use the net pots as a sort of "root basket" inside of other pots. Since it is not a tight fit, there is extra air space around the pot, regardless of the type of pot.
I do find that roots extending from the net pot do "stick" inside the clay pot, but this is no worse than just using a clay pot "without a net". I may try using the net pots inside plastic pots in the future, especially when things start moving indoors this fall.