The worst tool I bought was a medium sized (about 2 feet high, cylindrical) spray container for spraying weeds. The strap (just one) went over the shoulder and was attached to the bottle with two split rings.
I filled it and slung it over my shoulder. One of the split rings straightened under the weight, and the full bottle came down behind me and hit me on the calf, bruising it. If it had fallen at the front on my foot it would have broken it.
After that I tried another one (different make) and tied the straps as well as whatever clips it had. In the end I bought a magnificent backpack sprayer with pump handle attached. It's ergonomically much better, and works brilliantly.