I have and use both, depending on the situation.
My HPG Kit bag has Molle webbing on the front and I have attached both some blue force gear web pouches that I carry small items in, like a phone or 1911 mags, but also an old M4 double mag pouch from a former life.
I use the M4 pouch as a holster for faster presentations in Grizzly country, as I tend to do a good bit of hiking there and have not been impressed with the speed at which I can make presentations from the zippered pouch.
Once I am off the trail or close to a trailhead or around the hipsters/liberals that are everywhere in Montana and other places in the West (the bears need to do a better job) I can just slide the gun back into the zippered pouch and go on about my business.
My Glock 21 with heavy 250 +Ps fits perfectly in the pouch as well.