Anytime I ever get a package with one piece of tape holding a box closed, I would say more than 50% of the time, the tape is broken, or snapped in some way, shape or form. Packages are not treated nicely from point A to B, and the only packages USPS opens are "media mail" packages, as they are allowed to do so to confirm the contents are in fact "media" related(and they state as much in their shipping guidelines).
Having seen the pictures of the boxes presented here, there appears to be 3 seams, two along the sides, and the seam where the box is closed. To put one small piece of tape at the closure means that any and all pressure put on the box is going to cause it to break. It's not a question of if it will be smashed, but from which side it will happen from.
The closure is a link in a chain, and when that box is sitting at the bottom of 100 other boxes(hundreds of pounds of weight), the pressure will cause that tape to snap most of the time, as the chain is only as strong as the weakest link, and that one piece of tape is rather weak.
I would recommend a piece of tape the length of the sides(at the seams, as well as one length wise at the closing point, taping around the box entirely is best, but more time consuming). Also, be aware of weather conditions, as cold, heat, and humidity can cause a single piece of tape to come undone and get snagged, or just fall off.
I'm sure those wafer tapes are great for a box sitting on a retail shelf somewhere, but they are next to useless in regards to shipping packages that go through hell and back.