
I own this, the Envoy, and the Passport.
Based on the review citing BPA I called the manufacturer. They switched to a bottle with no BPA over a year ago so that is no longer a concern. The bottle and the package now indicate this.
Just the main compartment can hold a compact umbrella, wallet, cell phone, and key case with room to spare. The smaller front compartment alone is big enough to hold a wallet, cell phone, and keys with room to spare. A lot of capacity.
The pack seems very well made. Easy opening/closing zippers, sturdy material, comfortable backs, a loop on the bottom to which you can fasten something.
The Express (this unit) feels less massive than the Envoy when wearing it. The Envoy has more capacity but no water bottle holders. Effectively, if you need to carry a water bottle this Express may have more usable space than the Envoy since the Express has two very spacious top-opening compartments with a pocket in the larger one. These are in addition to the two water bottle holders.
If you want greater capacity and do not need to carry a water bottle consider the High Sierra Envoy. High Sierra Envoy Lumbar Pack
If you want a comfortable although small unit just to carry for example a wallet, cell phone, and keys then consider the Passport. High Sierra Passport Lumbar Pack.

First off, I'm glad Amazon carries this product -but I really wanted to physically inspect a number of lumbar packs, make comparisons, and decide if it met my capacity, comfort, and utilitarian needs. Unfortunately, I couldn't find any in my area stores.
As it was, choosing this particular pack was almost torturous as you don't get a clear idea of what it can hold. And so I kept vacillating between a few High Sierra products -this one, the Diplomat (which seemed too high and narrow), the Ridgeline (maybe to large?), and the Envoy and Passport (both of which didn't have bottle pockets). But in the end, this product seemed like the best choice.
The primary motivation for getting a lumbar pack is that I needed a mini diaper bag, something I could bring to museums, etc., with the kids and have full function of my arms and hands. Fanny packs didn't fit the bill because I don't want something bulky in the front as it gets in the way. Backpacks are size-overkill and make for sweaty backs in the summer.
That said, it's a nice pack with 2 pockets (one large, one small). For me, one holds a travel size baby wipe case, a few diapers and cream; the other, car keys, camera or flip, sunglasses. Not much more could fit maybe other slim electronic devices like a phone and iPod, but since there are only 2 pockets one has to consider what's going to be scraping against what.
The mesh bottle holders are nice -they are each designed with a stretchy loop that holds the bottle snug so it doesn't fall out. That's good but it also means that blindly reaching behind to reinsert a bottle is a finger-fumbling act. Maybe I'm lame, but I have to rotate the pack to the front to place the bottles back. The holders hold most any 16-20oz bottle: bottled h2o, soda, arizona iced tea, etc.. The included bottle is useless to me as it contains BPA -sort of idiotic given the chemical's bad press.
Lastly, if you need to access your stuff *often*, get a fanny pack -reaching behind or rotating constantly isn't convenient, especially if you have a camera in there.
Overall a well-made, comfortable, and useful product. Would recommend.
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A great entry-level pack, very practical and well suited for the casual/day hiker and/or anyone who doesn't want to spend $50-60 or more on a pack from a "fancier" equipper. The pack is well constructed and carries plenty of water. The central cargo container is modest -it's not going to work as a diaper bag -but if you're looking for a pack that optimizes H2O capacity (has pockets for two water bottles) without being a huge monster, the High Sierra Express is a good choice. For a slim profile, buy a second 500mL water bottle. Or if you need to reduce bulk in your luggage, leave the included 500mL bottle at home -the Express' twin pockets will easily carry two 1-liter bottled waters from any convenience store at your destination with only a small change to the balance of the pack on your body. (A 1L bottle is taller than the included 500mL bottle, of course, but the pockets are still deep enough to hold it securely.)
The High Sierra Express is comfortable to wear, not too heavy, and is narrow enough for even the most slender of users. The belt, adjustable from 18" to 55", is ordinary webbing, not padded -slightly less luxurious for long-term wear but also less bulky.
The High Sierra Express offers a great balance of overall size/bulk, water capacity, cargo capacity, comfort, and price! When I need to replace my second, older Outdoor Equipment lumbar pack, I plan to buy another High Sierra Express. :-)
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I bought this for half day hikes into Big Cypress Forest Preserve in South Florida. The belt is strong enough to hold three lens pouches for relatively heavy zoom lenses. The pack is big enough for a tighly rolled poncho, bug repellant, snake bit kit, compass, mirror, whistle, matches, utility knife, cell phone, notepad, pen, lens cleaner and lens paper, bandana, and a pound of trail mix. The side pockets easily hold two bottles for water. It does get heavy, especially with the lenses so I use workshop suspenders to take some of the load off of my hips. This is a nice alternative to a camera vest which can be pretty hot to wear; and a lot easier to use than a back pack. And it is very well made.
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I like the size of the compartments very roomy. the back compartment can fit a small paperback and the front compartment is good for keys, phone, etc. The fit is good with the adjustable straps. it is a comfortable, well-made product.