A far better alternative to an expensive Disklok, is a battery cut off switch.
Its a small connector that is easy to connect to your battery earth lead, and you just unscrew a special terminal that cuts all power to your vehicle.
To reinstall power to your car, you just turn the screw anticlockwise.
There is no chance of accidental battery drain, and its a cheaper alternative to a steering lock.
I have one of those bulky yellow disklocks, but have mislaid the keys to the thing, and replacements are nearly £60.
I agree that if a thief sees as Disklock on your vehicle, he is likely to look elsewhere for a vehicle to pinch, but what if your away from your pride and joy for several hours.
Its easy pickings, but with a totally invisible battery cut off switch, under your bonnet, most thief's would simply give up, if there's no electric going to the vehicle.
A cut off switch costs around £20, a Disklock costs a lot more.