I rate them, worth every cent.

As a windsurfer and surfer I spend a bit of time on here, I'm more of a reader than a poster. Anyway here is my two cents.
The reason I designed these straps is so I could lock my boards to my racks. My wife and I both windsurf and we always had multiple boards on the rack worth more than the car itself.
So do they work?
From a theft point of view -
Regular tie-downs - It takes someone 10 seconds without any tools and without attracting any attention to grab your board. They just pretend they own the board walk up untie it and walk off.
KanuLock tie-downs - A thief has to be prepared and have tools to cut braided stainless cables - yes it can be done, but requires planning, and in a public place, it would attract some attention being up on the racks with some bolt cutters etc..
Even locking your boards in your car is only a deterrent, anyone can smash a window with a rock.
Compared to tying your boards down with regular straps and hoping no-one walks off with it, the Kanulocks are a big theft deterrent.
Kanulocks as a tie-down- They work great! The wires in the webbing make it easy to throw the webbing (don't throw the buckle)over the board even when it is windy. They make almost no wind noise compared to standard straps. You can easily tie off the excess strap, you just use them exactly how you would use a regular set of tiedowns.
Denting rails? I have never had this happen, but I guess like with any strap if it is way too tight over a hard rail there is the possibility. I only ever tension my boards down with enough tension to stop them moving. If you are really worried use a board bag, or tie your boards with the fins facing down at the front of the car (that way the straps pull over the rolled top of the rails rather than the sharpe under edge.) I do this with some boards because it allows me to drive under our roller door with the fins in.

If you have a really fragile hard rail board and are still worried then get a small off-cut of carpet. Do this regardless of what type of straps you use.
Difficulty locking? The early models required a fair amount of tension to lock - the new ones (since about 2011) are super easy to lock, they also have numbered keys so if you lose them, you can call me and I can send you new keys.
Anyone with old ones get in contact and I can sort something to get you an easy to lock set.
Merry Christmas! I hope everyone gets some good sessions over the holidays.
Clinton