Personally I'd avoid using companies that can put the alarm as part of the deal for buying the house.
Get some quotes from SSAIB, ask them which systems they use,
The galaxy is made by Honeywell and is more expensive than enforcer, it's just what I'm used to fitting.
As others have said look into HKC and Texecom.
You would be better off with something like hkc or 12w etc as if you ever decide you want Monitering of any sort it will be easier to add.
Not that there is anything wrong with the enforcer it's a good bit of kit just may not be suitable depending on your needs.