I just borrowed a coworkers Sarris. Holds three adult bikes (although I think he converted it from 2 adult, one child). Not bad, I liked it. I did put the bikes as far back as possible, so that the hatch on my wagon would open. My mpg's took a big hit--looking at it, it's almost like towing a trailer. I almost think it might be worse areodynamically than bikes on top, as the bikes are pulled sideways through the air. But no lifting a bike onto the car.
The one thing I noticed was on my bike, where I have fenders, the Sarris requires partial dissasembly of the front fender. Not that much fun. No fenders, and I think it's a great setup. Fenders, and the top tube hold-down setup is probably better. My coworker has this high end carbon-fiber MTB, so he could not use the top tube hold-down setup.