Please explain to me when you install that bladder tank, how it will reduce the water pressure in the system?
Au contraire!It won't, it just becomes part of the system and is subjected to the same pressure.
Pressure is created by resistants to flow, and head pressure.
PV/T = PV/T
Take a long, hot shower, turn off all the water. The system is sealed now (i.e. no flow). There can be no change in volume. There is no resistance. Equilibrium has been achieve. The check valve (if you have one) will allow the pressure in your pipes to increase (i.e. more water comes in from the street), but not decrease (you can't push any water back out).
As the water heater works, it's heating up that water - temperature increases, but the volume is fixed, so the pressure must increase.
With an expansion tank, the temperature will climb, the pressure will increase some, but tank will expand, and increase the volume in system.
So, it does reduce the impact of pressure increase due to water heating, but enough to need it? I dunno, I can only explain the theory.