While a shoulder strap is a relatively good idea for any sprayer larger than one gallon, this strap falls far short of expectations.
First, the sprayers are designed with only one attach point. The user is expected to clip the other end of the strap on to the opposite clip. Poor design.
Second, and most disconcerting, the strap is entirely too short. If you're lucky you might get one arm through, but then the sprayer rides almost entirely on your shoulder blade. As a guess (note: I didn't actually measure the strap) the full length is no more than 14 inches. Doing the math, that leaves only a 7 inch opening for your arm. You can extrapolate out from there as to where the sprayer actually rides on your back.
I do NOT recommend this strap under any circumstances. Again, poor design and waaaaay too short to be of any use. Mine will find its way to the junk drawer. Very disappointed.