Hi,
I've been on escorted tours with Exodus and Explore (not in China though).
I think if you are a solo traveller, and for whatever reason are not keen on travelling alone, then these escorted tours are a good idea.
Benefits:
1. You probably get to see more in the timeframe, than you would get to see on your own (since you dont have to spend time finding out information)
2. Sometimes travelling alone, you dont get to meet too many people, so if you like company, at least this way you are guarenteed people with whom to chat.
3. You have no logistical worries, since Explore sort all this out.
Disadvantages:
1. In my and my friends' experience, generally these escorted groups comprise a couple of couples, maybe a single guy or two, and mainly single girls in their 30s. This might not be your idea of ideal travelling companions. Depending on the tour, the average age can vary widely too. (But beofre you book, the company can give you the age and sex profile of the other people going).
2. If you are travelling alone, you share a room with one or two people of the same sex. After a few weeks away, it can get tiring to never have time alone. On my last holiday I paid a supplement for a single room, and it was the best money ever spent.
3. Another disadvantage is that the tour leader picks the restaurants, bars etc, so you are whisked there, when perhaps you would prefer to try out somewhere else. I'd recommend going off on your own for an evening or two to spread your wings a bit.
In summary, I think its much preferable to travel with a friend (due to the freedom it gives), but if you want to go somewhere in the world in which your friends have no interest, then I'd recommend a group escorted tour.
Hope thats a help.