When you have a Fuel rail with injectors and run fuel pressure in excess of 20psi you will run into problems with "pressure waves"
Each time an injector opens and closes there is a pressure wave generated in the fuel rail at that injector, i.e pressure drops(injector is open), pressure returns(injector closes)
When there are multiple injectors these pressure waves can increase themselves as they meet up, like "super waves" at the beach
A fuel pressure regulator(FPR) has a "rubber" diaphragm, the FPR serves two purposes, it maintains the fuel pressure but also prevents pressure wave "reflection" so stops the pressure waves from building up in the fuel rail
A Fuel Rail Damper is just the "rubber" diaphragm without the Regulator part, it absorbs, instead of reflecting, the pressure waves
The vacuum hose on an FPR helps maintain an average pressure in the fuel rail based on engine load(high and low vacuum levels)
But its also there for safety
If FPR should leak fuel is sucked into the intake manifold instead of dripping on the engine, HOT engine, lol
Damper has the vacuum hose just for safety reasons
Dampers were used on Rangers in 1998 and up when the FPR was moved to inside the gas tank with the fuel pump, that's also when fuel pressure was raised to 60psi, from the 1997 and earlier 35psi