They're great for quick inexpensive packing but be aware that you may need a blade to get the flaps loose...the perforations on about 1 out over every 5 or so needed help.
Needed boxes for a move and Staples boxes worked great. With the handles built in and easy assembly it made the packing easy and the movers loved them.
One the best and less expensive storage boxes I could buy they are stable and strong enough to hold the files and document up to 35 lbs and stackable up to 4 boxes easily.