I just had a look at this feature for a trip coming up in late August. They claim that seats 11DE and 12DE on the 737-700s are emergency row seats, which technically they are, but they have no extra legroom. I'd be annoyed if I had discovered this after paying $15 for them. Not that it matters -- all the emergency row seats appear to be blocked.

The seat selector tool is also incredibly slow -- it took about 5 seconds for it to respond every time I clicked on my mouse.

More thumbs down from me.