I bought the mat, all 1.6kg of it. It's supposed to puff up to "about 5cm" thick, which it did as long as you count 4 as about 5. Denser foam mattresses can take a couple of days to recover their shape after being factory squeezed, so I've left it up with the valve open just in case.
I can't fault it for comfort, I was surprised how nice those 4cm felt for a brief test, though it kept making little crinkly noises even when I lay still. Probably just the insides settling, though I am a bit over the 110kg limit.
The rucksack seems pretty robust and weighs... less than the mat. (It was a bit big too big and floppy for the fruit & veg scale.
) The straps are held on by a large Velcro pad that's squeezed into a slot between the main compartment and the back padding, allowing for some adjustment but I wonder if it would creep upwards on a long walk. The slot might take an aftermarket stiffening board for those like me who like a frame.