I haven't shot anywhere near as many rounds through my PS90 as LES has, but I have had zero issues and loading the magazine is fairly easy, I wasn't sure how to do it at first either... LES helped out and so do Google.
5.7x28mm round is certainly an odd duck, some people L O V E it, some think it's a joke and not worth the trouble, I tend to like it, I only wish it were less expensive, I have been looking into reloading it as I have a bunch of projectiles, however they are on the heavy side for 5.7, 40gr. would be ideal, with the powder I do have.
About the only issue with reloading is crushing the case, removing the finish on the case or blowing up your firearm...
The 10mm I have are s great combo, I wish I could find extended magazines, but maybe I haven't looked well enough