Stop Tap Advice

I have a customer who wants to boost the incoming mains pressure with a SP21S ShowerPowerBooster so I wanted him take some pressure readings at his stop tap. The stop tap looks old and decrepit and my worry is if he starts messing about with it he causes a leak which ends up having to replace the stop tap. If he does replace the stop tap is there a like for like replacement stop tap he could buy:-

I don’t think you can get those anymore. They can be replaced with standard stopcock or lever ballvalve and pipework adjustments. Can you not obtain pressure readings from a garden tap, or washing machine connections?

The pipe splits 3 ways after the stop tap so I was hoping to get pressure readings before it splits so as to find the pressure drop for various flows in the service pipe feeding the property alone. I think he should replace the stop tap anyway as it could be the cause of the problem (if its corroded or obstructed internally). I want to advise him of the best way of replacing it. I can easily get him to take off his shower head and screw my test gage directly in to the shower hose to get some readings so I am asking him to do that anyway.