The Tactical Utility Pouch seems to be high quality. I can just barely fit full length mags in it, but it's very tight. The Velcro area for the top flaps are roughly just under 4''x2'' on pocket area, and 3'' by 2'' on the flap. The pouch is a nice size and would be good for carrying anything.
This is an excellent pouch - just not for full length magazines. These can hold nerf grenades very well, and the DZP MKII speed loaders also fit nicely. As for magazines, no way. 15 round full length magazines will not fit, and 18 round magazines never had a chance. For loose darts, and half length darts, this could work. There is one other review on these that says that it can fit 4 magazines. I have no clue how that is possible, maybe mine is defective and too small, I have no clue. For anything but full length magazines, highly recommend.
This will hold 4x magazines- 2x in each pouch! It will hold 18-dart stick mags, and hold them well enough that they don’t fall out too easily when running, but if you want the Velcro to fasten over them, you need to limit yourself to 12-dart mags or smaller (unfortunately). My only real complaint (other than the Velcro not securing over 18-dart mags) - is that the Molle straps are on upside down, so that the snaps fasten at the top. Since magazines aren’t that heavy, you should be fine- but if you accidentally push down on the pouch too hard, the snaps may come loose and you could have the pouch fall right off (which I had happen in my last HvZ).