I'd say most of my implements use the spline connection on the input. My snowblower used a shaft with a shear bolt. I used a PTO shaft spline to straight shaft adapter on it which saved me buying a whole new PTO shaft when I got the used blower which needed a new or rebuilt PTO shaft.I don't think I have any implements were that is possible. They all are bolted or keyed to the implement. Is it common to have a quick-connect on the implement side?
I added a PTO clutch on my wood chipper which converted it to splined shaft input.