I've had a pair of Side Arms for approximately 8 years in constant use. After this much use, I can still drive like a lunatic and not worry about the bikes on the roof. Awesome.
The older of my two SideArms doesn't really fit a 29" mountain bike wheel, but the slightly newer one does. Apparently they increased the length of the arm around 7 years ago. Wide tires fit, up to about 2.8", but that's pushing it.
What I would like to see improved:
Air drag. These racks make a lot of drag, in my Subaru, it eats around 1-2 mpg with no bike in them. They are also noisy.
The rear wheel strap always wants to be in the way while loading a bike. I tuck it under the aluminum v rail, but it can sometimes be tricky. A nice refinement would be something that easily holds that strap out of the way while loading a bike.