I was going to ask the same question I dont want to be without my immobilizer I do have a cat 2 fob but just the factory alarm as I dont have a garage its piece of mind not to mention sleep that my Blue is safe whilst parked up ect.
I think I was one of the first to get Kpro on a facelift, it was done at TDi north about 2006. I was given a loaner Kpro whilst mine was sent away and if my memory serves me right it wasn't a pre-facelift Kpro I think it was refered to as a wide band version. (During that time my ignition light was on) when my kpro arrived and was fitted I was given the option of having the factory fitted immobilser isolated. I kept it but now have two alarms on my car. I only need to press the aftermarket alarm fob though.