PS,

>I'd love to spend 10 days or more in London ...<

Then why don't you?

You don't need no stinking tour. :)

((I))

I took a Cosmos tour on my first trip to Europe many years ago, and had a blast. You don't have to apologize for choosing a tour.

As far as what the "upside" of a tour is, it's *much* less stress and planning for the first-time traveler, and for many people, that is a huge upside (otherwise, there wouldn't be so many tour companies doing big business - some people only travel by tour and that's fine for them if they like it).

Now I'm DIY all the way and can't imagine taking a tour, but I also don't regret taking a tour on my first trip to get my feet wet. (I was only 22 my first trip and my parents were concerned about my going solo, so the tour was a compromise, with a few free days in Paris added in.)