The size of the cross bars depends on which van you are putting them on. For the old standard Thule square bars, your 06 will take the 50 inch load bars, your '14 Odyssey will need the 58" load bars. To find the size needed/recommended for your vehicle, go to the Thule.com website click on "fit my car", and put in the year, then make, then model, select roof rack, then roof railing, then there should be 3 or 4 different products. The ones that you have in your photo above are the squarebar evo ones (for the 2015 the evo 135 comes up as being compatible), if you click on add to cart, then click on the cart in the upper right corner, the cart will show that you actually have 2 different products--a set of crossbars (thule calls them load bars), and a set of feet. The bars themselves retail for $129, the feet retail for $229. The link you have above are just for the 150 bars not the feet.
The feet are the parts that attach the crossbars to the roof rails.
If you are feeling adventuresome you could pick up a set of Thule 450 for around $80 on ebay (make sure that all the parts including locks and keys are present) and a pair of 58" square bars for $60-$80 including shipping. They may not look as nice as the squarebar evos, but they are very functional.
Also, do not be surprised at the howling that bare crossbars make. There is no appreciable noise when there is a cargo box or paddleboards or kayaks attached, but when it is just the crossbars it is a bit annoying above 35 mph. Our bars live in the garage when there is nothing on top of the van.
Just to be clear, one needs the roof rails to use the above stuff.
Hope this helps!