I'm have a Clifford Concept 600 installed.
Seems to work o.k., but the 'car-jack' option really is a pain in the ..........
You can disable it though, but why bother with such a option, when you probably better off with a cheaper alarm from clifford.
Personally i wouldn't go for the very expensive alarms, since if they want your car, they'll have it, no matter what alarm you have.
Here in Holland they have this "SCM-approved" label on some alarms (goverment thingy), which show on your window (little triangled sticker). I do know that car thiefs leave the car alone if it has one of these stuck on.