I saw a friend using this product as we prepared to take a group of Boy Scouts on a backpacking trip. The extra room the side packs provide is very useful for items you need for quick access. I use mine for rain gear, a lightweight jacket, and other items. Don't be decieved by the size of the bags, they are bigger than they look.
My Gregory Palisades doesn't have any outer pockets and makes it tough to access things like a water filter quickly. I attached the pockets to the side compression straps and I was able to store my water filter and small binos in one, and my MSR Whisperlite and 22 oz fuel cannister in the other. It also has smaller pockets that I put my compass and headlamp in. I had plenty more room. It is great for folks without side pockets who like gear at their fingertips. In 8 days in Yosemite, I saw no wear and the pockets stayed securely attached to the compression straps.
The small pack I have works great for short hikes but has no spot for water. These pockets can latch on to almost any place and will hold a nalgene bottle and have room for other items as well....the price includes both pockets as a set, a great deal for the price. Erik
I purchased this for a winter trip where I wanted easy access to some of the bulk that winter brings - spare gloves, hat and fuel. Pockets give great extra volume, they even contain an extra little zippered pocket that I was not expecting. I attached these to my pack with my side compression straps but the pockets get in the way of being able to cinch these and the pockets tend to flop a bit. I would still buy them again for the right reason.