dual zone shock v's ultrasonic

I am seeking opinions on the pro's and cons of the use of dual zone  shock sensors.

In the UK , most alarms use ultrasonics for interior protection. I am of the mind that a good shock sensor will offer better protection as ultarsonics do not alweays offer adequate coverage in the rear of the vehicle. I am thinking of installing some Avital products that have a built in dual-stage shock sensor. A friend of mine installs them and claims that if the alarm control unit is securly fixed to the body ( the way it should be in my opinion), the shock sensor does not perform well... If you cable tie the alarm control unit to an existing wiring harmess, the dual zone shock sensor works OK.

I welcome any comments - what do you guys prefer to use in the US.

Thanks

Naughtydog