A little fiddly, but works well - PODAVACH AR-10 U-Loader

The loading up of cartridges is a little fiddly, because the "fit" is loose. But once loaded up, the charging of the mag is quick. The mag wants to resist, so there's a little stiction at first, but once going it zips through 30 cartridges like butter. So, is it a step change in mag loading times? Well, certainly not by an order of magnitude. But this loader certainly speeds up the process enough to make it worth it, and it also saves you some callus building (unless that's what you were looking for...)