We used Hullivators on the top of our Prius all last year and they work as advertised, once the yaks are loaded in them. Lifting the yak from the lower position takes about 10 to 15 pounds of effort and - once in motion - is smooth and effortless in the follow through to the top position. Lowering them is just as easy and smooth.
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Without going into detail our Ridgeline wouldn't work with the Hullivator. So we went with the Thule Sliding extending rack mounted on Yakima Frames on top of the Ridgeline.
The Thule did a good job getting our new Oasis home. Due to the short bed ie higher angle, we had the yak slide off when we tried to remove it.

Getting it back on was a real problem and getting it off again more hassle.
So we traded the Thule rack stuff for a Malone Sports trailer, I would have preferred the trailer designed for Hobies, but one wasn't available. We were told by the dealer to buy the foam pads and put them on the Malone's cross racks and to latch the yak, upside down on top of the racks.
I wasn't comfortable with that concept, and a younger relative who has owned various boats for decades that have been trailered, said, "Don't do that!"
He recommended installing the Thule combo slide and load racks on the Monroe's cross bars, to get the yak up and then secure it across, then forward and aft and throw on a couple of other straps to secure the yak besides the straps that came with the Thule combo.
We did the above and latched the yak on top. We did some test drives around where we live with hills, curves and typical roads needing repair. The straps held the Yak tight.
We got the Thule combo pack on sale at REI, and I installed them with no problem on the Malone's cross racks. We had bought the wide track little Hobie wheel trailer and with it in the rear trailer holes, the yak went on and off the Malone, fairly easy.
I made a 10' bow line with a snap hook to attach to the bow. My wife helps to guide the Yak off and on the Thules and trailer with the bow line. I put the little wheeled trailer in and lock it when I can, to get the Yak off and to the water.
The little trailer worked well at a local lake where we had to transport the yak over a hundred yards over rough terrain to the lake and back to the parking lot. We loaded the Yak easily with the trailer and my wife using the detachable bow line.
A trailer is the way to go for this second childhood couple.
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My only issue in using the Hullivators is the transition from the cart to the cradle itself - not so bad with the Sport, but the extra weight of the Outback eventually caused me to throw my back out in late July and that was the end of the season for us. Oh, and be aware that your gas mileage will plummet with all that added mass on top of the vehicle; our Prius went from 56 MPG down to 31 while we had the yaks on top.
This year we decided to go with a trailer, and looking into that alerted us to the TI, so now we'll have a bigger, faster yak as well as the means to get it into the water without strain. We used the trailer for the first time last weekend (both days!) and it really takes ALL the strain out.