What are the differences, if any as far as quality, between the made in usa and the made in italy P320 magazines?

To the best of my knowlege the only issue with P320 magazines, other than some compatibility issues betweem models, are some complaints of difficulty loading the last round in some magazines. Mec gar makes the Italian sourced magazines while Checkmate makes the US sourced mags.

The only problems I have experienced is that the 21 round mags I bought relatively early on for my P320 RX full size won't fit my X-5 without some modification.

I have heard exactly the same thing about the difficulty fully loading Checkmate magazines.

I have both Checkmate and Mec-Gar P320 mags and can fully load both with a Maglula loader.

I have both(17rd) and not had any problems with either one. I do load with a Maglula with no problems.