....because its approved by the insurance companies.....therefore if/when the organised bike thief comes along and takes your darling, you can get a another one. And its strong enough to deter the opportunist crack addict who hasnt come so well equipt.
Fitting requires a proper 240v drill with a 16mm bit (about £8 from B&Q).
I had to replace the expanding bolts with my own from B&Q as the ones supplied fell apart in the hole. Annoying.
Anyway, team it up with an oxford chain and lock (also 'silver sold secure') about 25 quid, and you have something that the insurance companies will pay out on, or the grafting junkies will move on from. Spend a few quid a month on insurance and all in all a decent security set up (famous last words)