GGD, best to ask the insurer if they have an "approved" tracker list and you can chose from on there?
What I have heard on here - the discounts offered by the insurance companies are not much ... and also the "tracking" is not very effective most of the times. It has been more of neutral or negative experience than positive on here.
As Justin mentions above - usually the specialist insurance companies know how good the vehicle security is ... and they go as per that. A steering lock is a good visual deterrent.
There are many trackers available on the market. If your Cali is used regularly, then you would never notice the power draw. But if it is not, then IMHO, a ghost is a better option.
One of the Ghost installers in the UK
https://immobiliserdirect.com/ has a deal on ... to fit a tracker for free with an Autowatch ghost. May be an option to have that as an option ... along with the Ghost as the primary security device?