While devices are nice and neat to have, with the proper magazine loading technique, your own 10 fingers and two hands will load any magazine ever made.
Hold the magazine in your left hand, place left side of mag generally parallel to your fingers, front of magazine should be facing right.
Magazine should be low enough in your left hand so that your left thumb has no trouble depressing the follower portion of the mag, your ready to start loading.
With rounds in your right hand, holding bullet round from the front between the thumb and index finger of your right hand, place back/rim of round onto the follower and press downward vertically with the thumb of your left hand. The motion of your left thumb becomes down and left, the tension of pressing down then left causes the left thumb to catch on the rim of the cartridge and your leftward movement seats the round into the magazine.
As the left thumb is seating the round, the right hand situates the next round, which is placed on top of the first round inserted, generally just back of where the bullet stops and the brass starts.
Again the left thumb presses downward on the round to be inserted, you'll notice the existing round's (in the mag) nose will tip down, due to the downward pressure of the one in your hand that your left thumb is pressing down on, when the back of the round your inserting has sufficent clearance, as stated above the right hand releases control to situated the next bullet (between thumb and index finger of right hand) as the left thumb is converting the downward pressure into a left direction and seating the round.
As long as this method is used and you become consistent, with not only how the magazine is held in the left hand but also the way the right hand sorts and situates the bullets your loading technique will improve as time passes.
While mods need to be made, depending on the type, model or class of firearm used, this technique works with any magazine made, at least any I've ever run into.
I have seen and used the Lula and many mag loaders and not a one of them can match the speed of someone who loads mags in this manner. The right hand grabs and sorts as the thumb on the left hand (holding the mag) seats the rounds. When the right hand gets empty, it graps another handfull of rounds and the process continues till mags are loaded.
Position, consistency and coordination between your left and right hands are the keys to developing a proper magazine loading technique, from Uzi and Glock 30-32 round mags to en-bloc M1 Garand "clips" none are a problem for those with 2 hands and 10 fingers, that knows how to use 'em.
And you'll have more money for more mags or ammo and less weight to tote around as well as nuthin to get lost, (hopefully you'll always remember to bring your hands with you, their rather tough to forget).
Mike