Got one of the tapco ar mags a short time ago, and I have found it to be fairly smooth. I still like the Magpull Pmags better, but so far, the Tapco mags are in second place as far as polimer mags are concerned. They seem to me to be very similar to the Pmags, but without all the nice details like the integral mag cover and seperate channels for the right and left stack.
So far, the one I have feels sturdy and performs well. Since they are about the same price as the Pmags, I will probably not get another one because I still prefer the Pmags. If they were less expensive than the Pmags, I might reconsider, but then again, I would probably just stick to Braunells mags for my non-Pmag selection.
On a similar subject, I also picked up one of the lancer plastic mags. I have not yet tested it out, but at this point I am not impressed. It is cool to be able to see the rounds through the side of the magazine, but not that big of a deal. The magazine feels much less sturdy when compared to the Pmags or the Tapco ar mags. I plann on posting a short report when I get a chance to test this magazine out, but don't know when that will be.