Peter The reason I like Mega MA10 is because when you buy the matched upper/lower billet they come with a charging handle,and the takedown pins,and also the pesky detent pin on the front is already installed and so is the ambi bolt catch.....makes it easy peasy to start your build.
also it has a tension screw,so if ever your upper/lower gets any slop you can adjust for it,but Ive never had to do this....they are built so exact you can hardly see the line where the upper and lower come together!
money well spent and not that much more either than other brands :) Wash