I have had 1 year of experience with 2 sets of Hull-A-Port Pro carriers transporting 12 to 17 foot composite kayaks weighing 40-50 lbs each mounted on a 2012 Subaru Outback using the more recent Subaru factory crossbars. Mountings fit fine on the bars but I found it best to trim the small rubber projections under the crossbars flush with the underside to allow the best purchase of the carrier brackets to the bars. One is supposed to hand-tighten the screws to the main carrier using the supplied bolts which works fine to initially secure them, but a point of important advice is to further tighten the bolts with your favorite wide-mouth pliers or vise-grip tool a few extra turns. (Place a towel on your roof to protect it from scratching it with your tool) Then let them sit overnight or a couple days and then re-tighten them again since you will be surprised how much more you can tighten the bolts after your first positioning. Then finally use them to actually transport kayaks. My first trial run using them immediately after hand-tightening and driving at 60 mph for a few miles resulted in enough movement of the carriers on the crossbars to call attention to how inadequate it is to only hand-tighten the supplied bolts.
After ensuring an appropriate amount of tightness and rechecking them every now and then, I've had excellent success in using them. Using 2 systems on each side of the roof easily allows carrying 2 kayaks on top of a typical car roof remembering to keep them far enough apart such that the 2 kayaks aren't "kissing" in the middle after you deploy the J-bars and place the crafts in them.
Transporting a kayak in an almost vertical position, however, particularly if using a wider hull-style kayak, does pose more resistance to side-winds but just use common sense when driving and you can easily detect what kind of forces are impacting your car/kayak. Travel speeds of around 65 mph in calm weather are usually quite comfortable but if there are substantial headwinds you might want to take it more slowly. Conversely, a good tailwind allows you to move along that much more rapidly.
I know that I've concentrated a lot on how secure and safe these units are, and so far so good with no failures. The kit comes with everything you need. It has a pair of good tie-down straps with very thoughtful rubber protectors over the metal buckles which make it safe to throw them over the roof and then back over the kayak without damaging your vehicle. You can store excess strap length within a Velcro pouch in the bottom part of the carrier. Fore and aft ties with ratchet mechanisms are also supplied. I use Thule "quick loops" to attach those to the hood and back hatch which has made life a lot easier than searching for an attachment point underneath a bumper lying on gravel or wet ground. It may also be useful to have a step-stool available both at home and along with you to make the procedure easier since many vehicles will be quite high up to be dealing with these carriers.
I've had no experience so far with any other system so I have no comparison as yet, but I can definitely recommend this carrier when installed as noted above. My rating of a 9 vs a 10 is for the lack of the importance stressed in the instructions on a more secure mounting procedure.
