The source of hot water is an INSTANT gas boiler ( dont know if you r familiar in USA with that type of boilers) which turns on when you open the hot tap then you adjust the shower water temperature by just adjusting the mixture of cold to hot water . The thing is that you have to keep reasonable hot water tap opening otherwise the boiler will shut off .
This setting is VERY sensitive to pressure fluctuation because when the pressure goes down near to cut in pressure the boiler would turn off and you get cold water shock lolll then you have to keep changing the mixer handel to compromise between keeping the boiler on and the water temperature, while if the pressure is constant then you just set the mixer handel to one position during the whole shower duration.
I hope now that you appreciate the problem here lolll
Would that anti- scald valve solve this problem? and where you should fix them?
I already have bought the Pressure Reducing Valve but ould go for the anti scald if it is more practical