Not personal experience, but my sister & her boyfriend used them for a europe trip - her boyfriend has travelled all over the world with his for years, and he recommended she get them, so he must like them.
I looked at them, they seem comparable to the arkels (which I have) but maybe a little more strappy and a bit harder to get into - my sister's complaint was that it was a chore to get into the interior compartment, lots of straps & buckels, whereas the arkel is just one zipper and you are in, even if you have loaded on top.
the arkels are ridiculously heavy, by the way, i hate mine for that.
You can also just put a nylon strap w/fastex buckle around a pair of panniers to lash them together. the strap can be used for lots of stuff while touring, like strapping stuff to the top of your rack.
my strategy for travelling is to carry a very lightweight duffel bag and stuff all the panniers inside, creating one piece of (heavy, awkward) luggage. You can put the two handles of the duffle bag over your shoulders and carry it like a backpack. It sucks, but it meets the one-piece luggage requirement.