Body Armor is a pretty complex issue. I would like to know bit more than what seems available onlne.
Reputable manufacturers are careful to use the term "bullet resistant" over "bullet proof" and you don't buy the armor " off the shelf" .. you send in your measurements and it is made to fit, because that is important to insure the important organs are covered. And you have the option to buy inexpensive one time use trauma plates .. a non Newtonian plate that is normally soft and flexible that becomes rigid when struck spreading out the area of impact reducing blunt force trauma to the body.
I have conventional body armor, and I insist the family wears it when doing fugitive recovery or similar specific jobs where there is a high probability of getting shot at ... IIIA is good for most pistol rounds including 44 mag soft points and 9mm hard ball. My first big question is how big is the IIIA area of protection .. with a conventional vest, that is pretty self evident and pretty consistent, you wear it the same every time, it fits close to the body , all the protection is in a single layer next to the body.. it doesn't protect what is in your pockets ... My second question is does the bullet have to pass thru the outer fabric/padding of the pack pack farthest from the body when full and then the layers closest to the body or thru a side panel then the fabric closest?
3rd question Does it count on the back pack being full? or is that rating empty .
It advertises itself as only a few ounces more than a regular back pack .. that seems a red flag to me , or regular back packs inherently offer significant protection. Light weight has never been a selling point for soft body armor.
Soft body armor requires significant care.. in use the fibers wear against each other . aggravated by dirt getting between the threads and increasing the natural abrasiveness with each body movement.. Moisture, either sweat or water/rain breeds mold and deteriorates the fabric .. typically warranties re good for 5 years or less with proper maintenance.
Wearing body armor, even the newest tacticoolest stuff is a royal PITA .. but when you wear it critical areas are protected even if totally surprised .. but it is hot and heavy and not done for the fun of it except for the few truly demented or super paranoid or those that just want to be too tacticool / combatsexy for their for their own good... yeah I know .. one must suffer to be tacticool ...
How often do you carry your back pack , especially a heavy one , or one that should be relatively heavy because of the protection? would you go thru the care routine of carefully hand washing and dirt or gunk off it and carefully drying it between uses and keeping in a protective container between uses .. or would it get dragged around like my grand kids book bags and have all and sundry including things with sharp corners stuffed in and out of it and thrown in a corner or dragged thru the mud and puddles.
Also bullet resistant material is not, in and of itself, necessarily good protection against knife or machete .. there are additional layers of Kelvar added, using much tighter weave if you want that kind of protection.
Only you can decide what is right for you... just know, depending on care of the backpack , it's effectiveness can be seriously degraded after only a year or two.
These are also the reasons most "in the know" folks consider surplus vests over the internet worthless.
Care and maintenance of body armor
30 Things You Need to Know About Body Armor
StackPath
The whole book bag / back pack format seems to run contrary to best practices of care and maintenance... the hanging up the vest so fibers to not get all scrunched or distorted in climate controlled environment/ protective case when not in use and keeping it dry in particular.