I bought a pair of these a couple of years ago but hadn't used them until my Offa's Dyke walk. After a few days my boots started to leak having been OK for a number of years. My feet that day were soaking wet, so luckily I had put in the above socks in my rucksack as a last minute addition. I wore them for the next 5 days (sorry)! My boots had water in at the end of the day, the outside of the Sealskinz socks were soaking wet, the insides were dry and so were my liner socks, consequently so were my feet. Their advert actually was true! Well worth buying in my opinion.
There is a deal on the internet at the moment for £10, a lot cheaper than I paid!