I was intrigued to find this video review at The Vulgar Curmudgeon's place.
He's also done an earlier review, on the original, smaller toilet paper "tablets". Those may be found here, if you're interested, while the larger ones may be found here. There are similar products from other manufacturers, too; see some of them here.
I'd never heard of these things, but I have several friends and acquaintances who regularly hike in back-country areas, or go on hunting trips where they travel as light as possible. I asked them whether they'd ever used such products. Three said they had, and recommended them from personal experience. They said they weren't as comfortable as toilet paper, but got the job done, and the saving in weight and space in their backpacks were so impressive as to make the choice a no-brainer.
A fourth friend, however, added a cautionary note. He's from Minnesota, and hunts there in winter; and he's traveled to Alaska to hunt there, too. He reminded me that one has to dampen these things to get them to expand, and pointed out that in sub-zero temperatures, applying a damp piece of cellulose fiber to one's nether regions would be both exceedingly uncomfortable, and a potential health hazard if the damp material should freeze to . . . shall we say, delicate portions of one's anatomy. He reckoned the defrosting process could also be hazardous to one's health, given that the only heat available would be from a fire or camp stove. "What happens if the darned thing freezes to your tush, then catches fire when you try to warm it up to get it off?" he wondered. Once he'd pointed that out, I wondered the same thing!
If you've used these or similar products, please let us know how you found them in Comments. I might have to add some of these to my emergency kit. At least, living in Texas, the freezing hazard is likely to be minimized!