I do not like the diaphragm type. Pressure has to be pretty high to get a good wide angle spray with the brass nozzle, so over spray is common. I have killed some grass bordering bed edges because of it. I do like the Solo Backpack sprayers, but I have had better experiences with the piston type and the cheaper plastic nozzle.
I have used a Solo Back Pack Sprayer for 10 years now. There is no better one in the market today. I love how easy it is to pump up to spray, one pump to the other brands three will do the trick. If you ever use this sprayer you will not use any other kind. Cynthia M. Grounds Management Supervisor, City Parks and Recreation