Agreed, the Toad Ai606 is a very reliable and stable security system. Has some good features too. £250 is a good price. The RRP on them is £349. - Of course, I can do it cheaper still!
Only one comment on price though. In my experience I've seen lots of installations that are cheap jobs. Not 'jobs cheap'... Badly installed systems, no boot/bonnet switches, no/half/incorrect immobilisation, sirens in easily accessible places...
There are exceptions, but try to get recommendations of installers, and at the risk of generalisation, aviod adds in some certain 'performance car' magazines that come to you. From experience, they don't like coming back to you when/if you have a problem.
Tracker Monitor is the one that I believe is one of the better ones to go for. As I said before, this is manly due to the active Police support regarding vehicle recovery.
All the above, very subjective, very IMHO