I'm surprised it has only three zones. It does not seem to have telephone or SIM ability to call you and your keyholders in an alert, which I think is a very important benefit. Neighbours usually ignore sirens until they get annoyed by them.
It seems expensive for a DIY kit. As it is not professionally fitted and maintained, it will not be "graded" but your insurance co might give you a small discount. This can be awkward if they refuse to pay out unless the alarm was operative in the event of a claim.
The description says it warns you if a door or window has been left open (presumably it means of the two that have sensors on them) which might be useful if you are careless enough to leave the house empty and insecure.
It says it has 200m wireless range. I have never had a shed quite that far from the house but perhaps it will be useful to someone.
I can't see how much additional sensors would cost, IMO you need (at least) one in each downstairs room, in the garage, on the stairs and hall, and any room that is accessible from, say, a flat roof, drainpipe or balcony. PIRs are not cat-proof.
I like an alarm that can chime when an external door is opened. Mine does from the back door and garage doors, even when the alarm is not set.
IMO it is an advantage to be able to set and unset it from upstairs as well as from near the main door. Perhaps they sell an accessory keypad. All this will put up the cost.
I have used several versions of Yale wireless alarm, which some professionals and others sneer at. I find them simple and good value.
Wireless packages are handy if it is a rented home or for some other reason you need to be able to remove it easily and without damage. I once fitted one to an empty house awaiting sale, and when sold I took it off and sold the alarm on ebay for almost what it had cost me.