If the lid already has a PRV in it, I don't see any reason to get a second PRV.
I have Spike conicals with their gas manifolds fitted. Those are composed of a gauge, 15psi PRV and gas ball lock fitting. It allows you to add pressure, monitor pressure, and be sure the fermenter doesn't exceed it's listed working pressure level.
I also have the SS Brew Tech spunding valves fitted on the fermenters. I typically keep them under 12psi maximum while fermenting. I have a batch still fermenting that's at about 10.5 psi (according to the gauge on the manifold).
I DO cold crash and carbonate in fermenter with these. At most, I see less than two PSI drop from when I'm at 70F to 35-38F. Pressure when carbonating hasn't exceeded 12psi so far, due to the temperature I'm going to.
IMO, if you have an open/available 1.5" TC port on the lid, I'd get the SS Brew Tech spunding valve. Yes, they're not cheap, but they do a excellent job of things. They're also one way valves, so you will NOT get anything sucked back into the fermenter due to temperature changes. I do make it a point to have the Starsan in the cup above the holes in the spunding valve (where the CO2 escapes). That's easy to do with a small bottle of Starsan solution right in the area where these sit.
BTW, the spunding valve type they show for that setup is one that I've had zero luck with. I had much better luck with the Blowtie setups when using kegmenters. At least with the ones I'm using now, I can actually set the pressure level before fermentation even starts, with little, or no, pressure in the fermenter. IMO/IME, that's a better solution than hoping you have the screw set correctly. Otherwise, you'll need to charge the fermenter with CO2/pressure, and then set the valve and hope you have it correct.