I highly recommend this rack. I've got a 15'6", 72lbs tandem kayak that I hull and this rack keeps it perfectly stable. As most people say, you probably don't need the bow/stern straps, but I use them anyway.
The rack doesn't lock to the crossbars, but I still leave them on all summer. The folding feature is a lot nicer than taking the rack off each time you use it and the PFD latch is much more secure than Yakima's plastic screw/nut.
It's an expensive rack, but it makes traveling with your kayak much more enjoyable, and you'll probably use your boat more too.