When i got my golf it was a non runner. Alarm system had gone up the spout it was a cat 1 alarm and immobiliser. Was a nightmare to remove properly.
You get what you pay for with alarms / immobilisers. So my advice is go for the best you can afford. Oh, and make sure its installed properly. If its thatcham approved (cat1 or 2) you need a certified installer to fit it, otherwise should your pride n joy goes missing, the first thing your insurance company will want to see is a certificate of fitment!!!