plenty of circuit race cars over here use lockers. With good race rubber and good suspension geometry the understeer tendancies induced by the locked centre can be completely eliminated. Those settings are not really practical for the street though.

But then again, lockers aren't really practical either, as others have said. Ok if you just drive it weekends, but if it is your daily transport, think twice before doing it. You will have trouble with axles and centres in a street car, especially if you ever put any weight in the car (like passengers). U-turns, parking etc will put huge stresses on the axles.

the diff will hop around in low speed, tight corners, tyres will squeal and attract unwanted attention, and it will probably catch you out in the wet - which will be at least embarrasing, and probably costly. Plus it's illegal in Qld, and I suspect in most other parts of Aus.

anyway, go for a ride with him, and see for yourself.