Maxpedition and other tactical gear makers have been making bags with loop velcro panels for a while so finally we have some more options on how to make good use of them. Since the intent is that these panels will generally be in the interior of bags the retention security is low in favor of easier accessibility. Some quick breakdowns:
M4 Magazine Insert - Available in panels that hold 2, 4, or 6 magazines they are a simple tiered open top design. Can accomodate AK mags with a snug fit. I would make coverage slightly less, but generally a good balance of mag holding and leaving enough exposed for a solid grab.
6"x9" Insert - A simple velcro flap design works as somewhat of a general use pocket. Can hold a rifle magazine horizontally and has about 1" worth of holding depth.
6"x6" Insert - A slightly smaller simple velcro flap design works as somewhat of a general use pocket. Can hold a CAT tourniquet verticaly and has about 1" worth of holding depth.
Admin Insert - Coming in at around 9" x 6" it offers a slot config of: 2.5",1.5",1.5",0.75",0.75",0.75". The 2.5" is good for general small electronics, 1.5" for pistol mags, some flashlights, krill lamps, and .75" works well for sharpies, but thinner pens with keeper caps work fine as well. The holding height may be more than desired for some items, but works for most.
PALS insert - Sized at about 6" x 7" it offers 6 (6") rows x 4 channels of PALS webbing. These inserts work great to allow connections of PALS compatible pouches you wish to use that don't have velcro on the back.
Being an Extreme Gear Labs collaboration these designs are straightforward and solid. I'm happy to have more options now for all my bags with big ol' loop fields!