OK, well let's analyse it technically then.
What he is selling is a boost pressure switch. It does nothing to regulate the boost; it is just a 'safety net' in the same way that the original switch (calibrated to 0.8bar if I remember correctly) causes the ignition to cut out when the boost reaches this upper limit.
We all know that the boost pressure is set by the wastegate opening, which you can control with a bleed valve in the wastegate actuator pressure supply.
What he is trying to allude to is Electronic Boost Control (not fitted to the Uno, fitted in a crude form to the Croma Turbo) which is where the pressure to the wastegate actuator is electronically controlled (on the Croma Turbo, to give an 'overboost' setting under controlled conditions - full-throttle, limited time). Ideally, electronic boost control drives a solenoid to control the wastegate directly to modify the boost curve (the rate at which boost occurs, as well as the upper limit).
This pressure switch simply cannot do this. He may have owned Uno Turbos for ten years, but he is not understanding the full ramifications of what he says. Yes, you can melt a piston through overboosting, and yes, this pressure switch will prevent this overboosting from occurring. But the actual performance gains are caused by a bleed valve (or uprated turbo/actuator), not this switch.
I consider myself to be quite mechanically/electronically minded

but if anyone would like to correct me or add more info, please do!
-Alex