Yeah, I have heard of them, I just moved here from the Rochester, NY area in the fall, we used to paddle the erie canal a lot and some bays off of lake ontario, I haven't even put them in the water here, the weather has barely broken, and just as I say that, it's only 50 degrees today!
I had the J bars on my explorer and with a long boat, they bounce around way too much for my liking, these things are acutally easier to load and they are rock solid when you strap them down. I'm a pretty tall guy 6'4" so working the straps isn't so bad.