The one you have showed from halfords is a mechanical isolator switch so you have got to lift the bonnet everytime you want to isolate the battery .
This is what I have fitted , it works from a small remote fob. Yes it will isolate your alarm as well , it will isolate everything on the car , these cars just do not get pinched , let's face it most people don't know what they are and they don't make a good getaway car with only 2 doors 😉