Rock solid... but be careful where you park your car afterwards...
A bit awkward to get the bike up on top of the car, so hopefully you are tall or your ride is low to the ground. But once you get your bike up on this it ain't going nowhere. This system locks the front wheel nice and tight, and works fine with my disc brake mountain bike.
Mounts quick on my Yakima crossbars, so quickly that they might as well have painted "steal me" on the side of it. Will work with the accessory lock housing if you use a nut/washer combo and thread the bolt down through the crossbar mount, however nothing in the instructions mentions this possibility.
I still highly recommend this bike mount, however given how expensive it is Yakima really should have included a better way to secure it to your crossbars so someone doesn't walk off with it while you're out on the trail (thus why I give it 4 stars instead of 5).