Pros: Simplified, yet well thought out. Has everything you need in a baby backpack.
Cons: You can't reach the daypack while wearing the backpack.
Since having my baby 6 1/2 months ago, I've discovered my inner gear geek. So believe me when I tell you I researched the backpack thing thoroughly (as I have the stroller thing - see my other reviews for my thoughts on that subject).
I tried on various models of Kelty backpacks and got a Kids Only Piggyback REI from a friend, in addition to ordering the Evenflo Trailblazer.
I picked this one because it comes with a sun /rain canopy attachment, which I thought would be useful for southern California. It also fit my frame (5'4" female) very comfortably. I found the Kelty's awkward to adjust and very uncomfortable. Perhaps a tall man would appreciate those more than I did.
Compared to the REI and the Kelty's, this pack is a much more streamlined, smaller design - better for wearing around your house for chores or for hiking and ducking under low lying tree branches. Evenflo has taken all the ideas of the fancier packs and provided them in this pack, but in a more simplified design. For example, the REI pack has adjustible straps galore, but the Evenflo offers 5 positions easily adjusted by a plastic button on the waist belt. Just don't adjust the wasit belt height when you baby is in the pack. The plastic buttons will break, as they did for me. (Evenflo sent replacements right away, for free).
The harness for the baby is much simpler than on the REI, but I think it's safe enough, unless you plan on doing cartwheels with your kid. It's plenty padded in the kid compartment and the kid doesn't ride too high, so you don't have to worry (much) about your child's head banging into tree branches. The other items are also easily adjustible so it shouldn't be hard to get a proper and comfortable fit. The sun canopy attaches simply and provides decent, but not full coverage. The front snaps for the sun canopy are hard to do and could have been designed a bit more generously. It does retract easily, much more so than on the REI model. I would still recommend that you stick a hat with a brim on your kid because low sun will hit from the front. The canopy is okay in light rain, but your baby's legs will probably get wet if you don't have an umbrella handy. One final word on the sun canopy - it's well designed so that it doesn't stick up that high, unlike on the REI pack.
You may not find it that comfortable on the shoulders after 2 hours, as I did, but that could be the result of not adjusting everything exactly so. The REI does have more padding and adjustment options, but it's also a much bulkier backpack.
You can attach toys to the toy loop, but my daughter enjoyed chewing the toy loop directly and when she conked out, the toys just made deep indentations on her little face.
The main problem with this pack, as will all of them, is that once you have it on, it is impossible to reach behind to the daypack for a water bottle or kleenex or what have you. It's there if you need it, but you'd have to remove the entire pack in order to get to it.
The Evenflo instructions tell you to have someone assist you in putting on the backpack. This is patently ridiculous if you're on your own with the child. You can put it on a couch or the floor and do it while the kid, but be careful that she or he can't kick it off balance before you lift it off.
I would suggest that you get a pocket mirror and tie it to the front straps of the backpack or keep it in your pocket so that you can see and interact with your child. I would also suggest that you stick a rolled up cloth diaper or small towel in the front of the child section to provide a pillow for your child's head when she falls asleep. Kelty sells an insert for their backpacks for $15, and it may well fit, but you can check that at an REI store.
Basically, this pack is identical to the Evenflo Trailtech, which is the cheaper model. However, the Trailtech comes with the slightly better detachable day pack - which has side water bottle mesh pockets - not that you can reach them anyway. I think the sun canopy is the only thing that makes the Trailblazer more expensive, though you should check that out yourself on their website (www.evenflo.com)
My pediatrician said it was okay to stick my daughter in there as soon as she sat up with assistance. The packs say to wait until they weigh 17 lbs, but since she's already nearly 7 months and barely 14 lbs, it could be a long time until she's officially ready. We've been using backpacks since she was about 4.5 months without a problem. She loves being up there and neither the Baby Bjorn nor the sling are comforable for long walks on the beach any more.