I do have a CDS prism finder, not the PD prism finder.
It works well except:
1. It is said that it is center weighted, but is close to average.
If I recall it correctly the new PD prism finder (the plastic outer cover one)
can select spot and average metering (I dont have it so I cant comment on this).
2. The center match needle movement of the analog meter is relatively small against the light change and the (shutter speed) adjustment dial angle change.
Well I got this CDS prism finder about $20 so I am very satisfied.
Note that this CDS prism finder takes two (2) SR44 silver oxide cells.
You may can use the alkaline equivalent LR44, but SR44 is better for voltage stability for this application.
(The new PD prism finder takes the 6V one if I recall it correctly)
If you are interested in this CDS prism finder, I will recommend checking the accuracy of the meter (for the entire range of light intensity) before you buy since CDS may drift by age.
Note that you must attach the CDS prism finder to the body to activate the circuit of the meter (there is a switch that sticks out from the bottom, and when you attach the prism, the switch will turn on). Also you must turn on the slide switch, which is located on the side of the prism (which is quite obvious).
I often use with the Polaroid back with Fuji 100 speed color and 3000 speed B/W instant film and my prism meter works fine with these exposure sensitive films.
Note that any RB prism is heavy though.
However, I only use RB67SD with prism only (metered and non metered, never use waist level) and handheld only.