does this tool look any good?

Unfortunately there's a large cost factor involved, the ones that will read and clear e.g. Bosch, Snap-On etc. start at around £4000 ($6000) and up. A) Get friendly with the dealers (good luck) B) I've got to speak again with my Snap-On guy, there is equipment coming out soon that should be cheaper. Look at web sites in the UK such as tooled up. The advantage of the Bosch is it contains circuit diagrammes. As for alarms in the UK, frankly unless they get R/S going in this country you're flogging a dead horse! Your ears should tell you how well you've installed an amplifier set-up, e.g. clipping, phase cross over points etc.