For our friends in restrictive states, California and NY come to mind. The restriction to 10 rounds is on its way in Calif, I personally like genuine magazines, especially the 20 round for AR and the 15s for the carbine. They seem to work better and last longer. There is a company called Magblock that makes and sells plastic spacers that will limit the magazine to 10 rounds. I sent off for some of these and they are about $4-5 each. The carbine 15/10 seem to be the easiest to install. The 20 round AR M16 blocks are specific to manufacturer, so you should let them know what the magazine is: a Colt, Adventure line, etc. The law accepts these if they are installed permanently using a spot of epoxy or screws. I'll leave those details up to you. I haven't installed any 30s yet as it seems a waste of time for what I do. I've never tried any of the foreign made 10 round mags, but I would imagine that Magpul work fine, I just like the size and shape of the 20s for offhand shooting. I think that getting foreign carbine mags to work well is not easy.