We got ours 6 months ago. No sign of any sticky stuff leaking out of them. Before swelling up, the contents feel like a powder, so maybe they have changed how they are made. I like them better than large blocks of ice because of their flexibility - the bubble sheets bend around corners and things and give more options on how the cooler is packed. A sheet or two will not last long - it isn't magic - the more cold stuff (ice, Techni-Ice sheets) you put in, the longer things will last cold, but the less food/beer you can keep cold! We have settled on 4 sheets, pre-cooling the cooler with a couple of 2L plastic containers of ice the night before, and it lasts about 3 days quite cold (depending on outside temp of course). As others have said, the colder you make them (not just -4C, but colder if possible) the better. And the lack of any water sloshing around (which can happen even if your ice is in "sealed" plastic containers) is a big factor.
Cheers
Oddy