The problem with booking my own flights is that if something goes wrong I have to solve the problem myself. If GCT makes the reservations and the flight is canceled or I miss it for some reason, they will rebook for me. Since I'm traveling solo, that's important to me.
When I went to Russia last summer, I was offered three different flight plans. The standard one was changing at Heathrow, which is not as much of a problem now that Terminal 5 is open. I was also offered one changing in Frankfurt for a slightly higher charge and another one changing in Amsterdam for an even higher charge. Amsterdam would be my preference, all things being equal, because it's a user friendly airport with nice helpful staff. However, I opted for Heathrow.
GCT now has a plan whereby they will customize the flight arrangements for a fee. I'll be curious to see how that works. I have already booked my trip for next summer to England, Scotland and Wales; and someone will be calling me next month to discuss flight arrangements. Very early in the game, I know, since they don't make up all the schedules this far in advance. But I don't see why I should have to change within the US when I'm flying to Europe and I live on the East Coast.