Yeah I have a Datatool, ummm... System 3 or something like that. It was dealer fitted when the bike was new. It does give a bit of extra peace of mind, although it can be a pain when working on the bike because you can't turn it off entirely - it beeps every minute to say "hey i'm turned off here". It doesn't appear to drain the battery much either. Actually had no problems with it at all, apart from the LED that corroded and broke off, which I simply replaced (with a cool blue one
).
It's not a substitute for a strong chain and ground anchor. Any thief knows that alarms can be defeated just by setting them off a few times, after that everyone ignores them.