I have that one bolted onto the house brick work to get it off the ground. Not that high up but enough to stop it being in the way and harder to attack.
I'd personally not trust that, myself.
Anything I can destroy with a single, decent swing from a 16lb sledge is not good enough for me.
Can you recommend anything in particular?
I personally had an Acumen Cat-3, which I fitted myself and backed up with a Xena alarmed disclock.
Cat-1 products (alarms and immobilisers) are best fitted by a professional, unless you feel supremely confident in doing your own wiring and don't care about the barely-worthwhile insurance discount.
Datatool are pretty popular as well.
Generally, I'd just suggest anything that is Cat-1 and Thatcham Approved... preferably loud as hell, too!!
Hearing that immobilisers/alarms can be hard on batteries would be a worry normally but I ride at least 20 miles every day sometimes a lot more, meaning my battery is always being topped up
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should be ok?
If you spend some of that time at mid-revs in order to charge your battery, it should be reasonably OK. It will always be a concern on little 125s and the like, though. If you can discretely run a line out to the bike, you can always keep it trickle-charging on an Optimate or similar.
Back when I parked on the street, I actually used an Oxford solar panel charger!