DGX Trim pockets, with 1 # weights.
1 x 1# weight turned sideways:
As someone noted earlier, they do mount horizontally. So, they would possibly be pointed down when you are in horizontal trim. My solution for this is that I mount them on my tank straps. I orient them to point at my back plate and I slide them as far down/forward as they will go, so they are pushed up against the back plate. They have really big pieces of Velcro to hold them closed. But, if they were to somehow come open, I think the back plate would block the weights from falling out of the pockets.
Of course, you could mount them the other way, so they'll be pointed up when in horizontal trim. But then a weight definitely could fall out if the Velcro flap somehow became open (and you turned yourself somewhere near upside down/face up).
If I were using them on the waist belt of my harness, I would probably orient them to open "up" when in horizontal trim, and then possibly also use some bicycle inner tube to put around the whole pouch once the weight is inside, to ensure they stay closed. But, the velcro area is so big, I really don't think I would feel like the inner tube was needed.