Bought a pair of these the other day. Firstly for what they are, they are a ripoff! 6-7 bucks for a pair of injection molded pieces of plastic made in China? I bet these cost Lowes 6-7 bucks per thousand. Hopefully HF will start making something like this and charge the correct price.
Anyway, I tried these in my toolbox at work and they seem to work OK, but with the major problem that the pair either needs to be connected, or the horizontal mounting surface needs to be larger. I loaded them first with a small set of wrenches, 8-18mm, and the weight of the wrenches alone was not enough to keep the rack from falling over when you close the drawer or roll the toolbox. I then loaded it up with a full rack, 6mm to 24mm, and got better results. Simply closing the drawer didn't knock the rails over, but rolling the cart over a big bump would do it. I will say that it fit the wrenches nicely, I like this style better than the snap in "handle" style that usually comes with a set of wrenches - easier to grab a wrench and they aren't as picky about size.
So main complaints, ripoff for what they are, but if you connect them with a strap of sheet metal or maybe double sticky tape them to the bottom of your drawer, they would work well.