This has been used for commercial fishingboats for decades.
You need a gearbox to get reduction and a clutch to stop the propeller if you get rope/line/net in the prop.
To set the pitch of the prop there are more than 3 systems going :
Most common(system 1) I think is the one with pitch rod, here the prop shaft is hollow and a rod inside is moved f/b to adjust the pitch. The rod is actuated by a internal hydraulic cylinder inside the gearbox, or by an external cylinder(system 2) in front of the gearbox (system called OD, don't know what this abbreciation is).
System 3 has the actuator on the prop axle, moving the outer part to adjust pitch with the internal part connected to the gearbox.
For bigger propeller the pitch actuation system can be in the propeller hub, with activation by pressurized oil, but this I think is for propellers over 2m diametre as the hub get quite big.
As for prices, these are for engine about 100kw : CPP prop, axle and stern gear about NOK125000, CPP gearbox about NOK140000-200000.
Prop with fixed adjustable pitch(dive to adjust pitch:-), axle and stern gear is about NOK110000, gearbox with reduction, forward/reverse, trolling valve : depending on brand and torque, in sum this system is cheaper and might be easier to get parts for depending on where you are.
Well known "local" manufacturers of CPP system :
Kumera/HVP gearbox and Helseth props
West Mekan Produksjon AS - Controllable pitch propellers
Nogva gear - Nogva Motorfabrikk AS
Benefits with CPP? Not only correct pitch for actual load, but also the ability to have higher revs to get more pump speed(water, hydraulics) and still maintain the choosen speed. Most trolling valves have a rpm limit of 1000-1200 revs, exceeding this might burn the clutches. With CPP you can move the boat 1mm forward/astern, I have never seen any other system able to do that...
Response time in my boat, from full pitch ahead to full pitch astern is about 2 seconds, and this can be done with full power.
If considering to buy CPP, please note there are differences between props regarding how far the pitch rod have to move to get full pitch, very important when choosing gearbox/OD.
Hope this was of some interest/useful information, please reply if You know of other gearboxes suitable for CPP.