Excellent small pack for hiking or summiting
I have used this pack for both day hiking and as a summit pack on backpacking trips - it works great for both uses. Its size is just right for a small first aid kit, water, food, and extra layers. The outside mesh pockets work well for quickly accessing needed items (water bottle, snack bars, map, etc.). With the foam back pad removed it compresses well using the three external compression straps built into the pack. This is a great feature when the pack is used to store clothes or a sleeping bag inside a larger backpack. The materials used make it much more durable than the other compressible packs I researched. I would definitely recommend this product.

light, comfortable & just enough room
I was a little worried that this pack would be too small and too flimsy for the day hiking I usually do, but in fact it's 20 litre capacity is almost the perfect size for an emergency kit, rain gear, lunch, and water. The mesh cages work well for stashing your map and water bottle, and the lid compartment is big enough for a thin book, camera, compass, and a few other odds and ends. The pack's light weight belies its sturdy construction, and there are plenty of ways to adjust it to make it fit you just right. It rides comfortably in the middle of my back (I'm 6'). The shoulder straps are very comfortable, but the waist straps fall about 2" above my hips and so provide little support other than keeping the load close to my back. A removable foam pad separates the water bladder sleeve from the main compartment. But the pad offers little extra support, and I found it stiff and bulky, so now it sits in the bottom of my closet. I haven't found any way to tuck the whole pack into its own lid, a cool feature of the other Marmot Kompressor models. But for lightness, comfort, cost and capacity, the Ultra Kompressor is becoming my favourite piece of trail luggage.