I went on this the first time they did it, and it was really good. That time there were reasonably few people and we got to walk on the synchrotron floor, peeking into the experiment places and stuff. They didn't really know what they were doing in the way of visitors, or what to expect, so it was quite personal and almost ad hoc. Very interesting, a great day out. I think it was a kind of beta test, because...
We went to the next one as well, but by then it had turned much more commercial, there were massively more people and queues for everything. Access to the synchrotron was essentially just the upper walkway. It seemed much more targeted at a day out for kids and parents rather than as showing geeks what they do.
Despite that, if you haven't been to something like this before it is great to see the engineering close up. I don' t mean the synchroton per se, but the way cables are routed, the labeling, fittings, etc. It is grown-up infrastructure you don't often get a chance to examine and see how it should be done.