That one looks good.
I have a big criticism of a lot of dog packs out there that they're just worthless.
REI Dog packs
Look at all the models on that page and compare the strap layout to the model you posted (it's there, too).
ALL of the other models have a single strap across the chest and no more than two underneath the dog.
The one you posted has a y-shaped yoke at the chest.
In my experience, the ones with 3 separate straps are JUNK. They rotate around the dog, especially when the load is off-balance, but also even when it's not. That chest strap also rubs on the shoulders. I used a Kelty for my dog (which looks identical to the Mountainsmith ones on that page) and it was TERRIBLE.
The pack I currently use for my dog has a y-shaped yoke at the chest and it's obvious how much more comfortable he is with it. He runs and jumps and just has a much easier time getting around with it. The one I use isn't made anymore, so recommending it wouldn't be worth anything. However, the harness and saddle bags are separate pieces. It's got a really solid leash attachment (another criticism of mine regarding other packs...leash attachments are often weak points) and the saddle bags are removable in case you want to use just the harness, give your dog a breather on a hot day, or in case the dog gets hung up in thick brush, the bags break away letting the dog get free. The harness is also custom made for my dog. I had to take probably half a dozen measurements for the harness.
One drawback to this pack is that the saddlebags kinda hang there and can flop around if they're not very full. The one you posted resolves that issue. It's nice and compact. I'd get it and give it a try. It looks worth it.
If my other dog wasn't such a whiny wuss on the trails, I'd probably get one of these for him. But because he hates long walks, let alone running with the bike, I'm not going to buy him a pack just yet.
