They are by far the best visual deterent you can get.
But keep in mind, that if someone is REALLY keen to steal your car, then they will.
The only quick way of getting a steering lock off is to cut the steering wheel.
When it comes to car theft, the only thing you can do is slow the thieves down.
The more things you put in their way, the more likely they are to move onto the next car.
Without a doubt, go out and buy one, but don't rely on it as a sole form of protection.
Some people think "I have an alarm so I don't need a steering lock" well..... it's those same people who come along and say "My car has been stolen, i had an alarm..."
It's pointless relying on just one form of protection.
Think like a criminal...... if you went into a car park, and saw a 200B with a steering lock, a Cortina with a big dog, and a Skyline with an alarm, which one would you choose to steal?