Is there a downside to using the Yakima Boa short tray type carriers? These use a fork mount and seperate short tray for the rear wheel, rather than a single continous tray. As long as the rack bars were within the correct distance for a normal bike, it seems it would function just as well....?

I plan to use them to carry mtb's / road bikes VERTICALLY on the back of my VW van on a rack like this: