It seems like hit & trial method.
If it works, then it would be great.
Can you ask him to show you some Mehran/cultus/Khyber where he has replaced the vitz’s ac and its working fine? If he has done some experiments, then its good. Check by yourself the cooling of the car where he has done such experiment. If you are satisfied with the cooling, then take your decision.
BTW, Mehran’s OEM fitted never seems working even good. Its performance is always lower than average. Specially during day time.