I've never understood the safety claim though. Fair enough if you squeeze and barge your way to the front of the traffic and want to be away before everyone else, then there's a chance it may be safer but it would have been much safer to have held your place in the traffic queue.
Then I got one today, I was sat in a completely clear ASL when a guy on a mountain bike comes past me and sits as far out into the junction as he can get without being hit. The lights change, he sets off at oh .5 of a mile per hour and cuts right across my path!!!!
I don't understand what he gained apart from a very large, swearing cyclist behind him.