I've used several different kayak trolleys during my expeditions, and the Mark 6 is definitely the best all round trolley for the simple reason that it rolls reasonably well over most surface conditions like gravel, grass, and compacted sand (on soft sand you are out of luck), and it is small.
Anyone who has done a solo multiday kayak expedition knows that the trolley is both an essential piece of gear, but also a pain in the ass.
The trolley is essential because if you need to portage your kayak and gear from your landing point for anything more than a few hundred feet, it can be a monumental effort to do it on your own. But the most trolleys are also bulky and take up a huge amount of volume in side your hatches, greatly restricting what can be packed with you.
Many times, I have wondered if there might be a way to plan my landings in a trip to eliminate the need for a trolley, but there is always a place or two that you just can't avoid.
The Mark 6 is the smallest trolley I have found so far that can bear the weight of a fully loaded kayak (you put all the gear inside the cockpit to keep the mass as much as possible over the wheels), and breaks down into a modestly sized package that will fit in the back of the stern hatch with enough room for the rest of the gear. You can also, with a little bit of puzzle solving skills, get all the pieces through the 8-inch day hatch of the Rockpool Taran, except for the wheels.
My recommendations on this trolley are that you should get the 10-inch foam wheels to avoid getting punctures, and two straps instead of one so that when you inevitably hit that bump on the road, your kayak won't fall off the trolley and god forbid, get an ugly scratch.
Also, because KCS is based in the UK their site didn't have the option for international shipping last time I checked. You should email the owners to make shipping arrangements.