Better than a simple throw on cover as no direct bodywork contact.
Utterly useless from a security viewpoint other than hiding the style of machine but a knife and a quick peek from an unscrupulous scrotebag will be all thats required.
If using off your premises i'd recommend a metal shed or one of those titan secure jobbies, excellent but pricey.
If on your premises then yes, better than a straightforward cover but not as good as a shed / garage as you will get moisture / condensation probs.
Decent price too, would suggest if you get one you bolt it down if your garden is windy.