I booked the BC in May through a TA, but then added a couple of extra nights at WL through
Undercover tourist. No rooms were available on the Disney site and I got about 30% off rack rate through
UT. I got my confirmation immediately and was able to link it to my Disney Experience right away. I got an email from Disney the next day. It's been a good experience. I've bought tickets through them many times. I'm glad to see they are offering discounted hotel rooms. They also offer discounts on non disney hotels. I noticed the Hyatt at the airport was 171.00 on their site and 225-250 on other sites. We're arriving late and staying the first night near the airport so I may book another room through them.
I really don't see any disadvantages to booking through them except you cant modify or cancel online, but since your trip is so far off better rates may come out. I would keep an eye on it. The week after thanksgiving is usually a slow travel week.