So, after getting some UZI magazines and got them converted for my 9mm AR i started to look at the Swedish Carl Gustaf 9mm speed loaders.
I have modified one speed loader and it now works great with one of my converted UZI magazines. Good thing in Sweden is that those 9mm ammunition clips can be found for free in almost every shooting range since people doesn't have any use for them after they're stripped of ammo.
I have seen both speed loaders and clips for sale in the US as well. (or at least in the past)
I have not tried this for a metal form magazine yet, as soon as I get one I'll try.
If you're tired of loading your magazines by hand one round at a time, give this a try if you can find a speed loader. I have also seen this type of modification for other double stack 9mm magazines such as the one for Mp5.
Modified to the left. You can see material taken out in the front and on the sides. I have also put some plastic in the rear to push the magazine forward some for proper alignment.