I wouldn't worry about the sturdiness of it...the little rubber covered ends that flip up to hook it around the seat post and stem seem to be pretty secure when they're in the locked position, and the tube itself is solid. I just make sure that the word "Yakima" on the tube is right side up so that even if the little locking levers come undone, they can't open up and let the bike fall out. You can use my extension tube if you live near Washington DC.
I'll look into that one. I saw one a the bike shop but I didn't study it.

Does it make it harder to secure the bike (as in LOCK) the bike on to the rack with a cable lock? Since we travel all over the place, I'm afraid of my bike being stolen right off the rack. I always lock them (mine and my son's) through the wheel and frame onto the rack.

Thanks for the answers!
Karen