My agent is booking our flights through ABD now, and I selected our exact seats. I think seat selection is more of an issue depending on what airline you book and whether or not that airline allows advance seat selection. For example, when flying to Germany last year, we could have booked a code-share flight on Lufthansa through United. I could not have selected the seats even if I had booked the ticket myself (that option was not available on the United website). My impression was that Lufthansa was blocking the seat selection.
With KLM, I just went through the flight selection process on their website like I would if I was purchasing the seats myself. KLM does let you pick seats, so I did so and passed the seat info over to my agent (who is working with ABD to get it done).
I found the lowest price through KLM (not ABD), but unless you are doing a search using a big travel search engine, there might be flights out there at lower prices that you just never see. Also, KLM gives a small discount (for us it was $68) on the price of a child's ticket. That was enough to almost pay for his $76 extra leg-room seat upgrade.
The reason I go through ABD is because I want the peace of mind that if ABD cancels the trip, I will get a refund on my airfare. In fact, when ABD books your airfare, the charge shows up on your cc as a charge from Disney (not the airline).
