These things are sweet! Are they relatively rare?
Yeah, they are awesome. they max out at 100 mph at 10,000 RPMs, handle really well, and look good doing it.
I don't know how rare they are. They were only sold for three years: 1972-1974, inclusive.
The 350 twins, CB CL SL, were sold for many many years, and there are probably 100s of thousands on the road.
The fours maybe benefitted from the twins' success and the cool factor of the 750 sohc/4 blended into one bike.