Op here: I've slept in tons of these things on the AT and on local trails here in new england. It's not weird compared to a tent. It can actually be easier and in some situations better (like when it's pouring rain or snowing). It can certainly be more efficient as you don't need to set up or break down your tent. You just wake up, eat, do your business, jam everything in your pack and take off. As far as critters: absolutely, yes you can run into some issues, but more often than naught it's pretty stress free. Down south during the thru hiking season some of the shelters had lots of mice, the occasional raccoon and of course bears (only at certain spots). I spent the night in a shelter just south of the NOC which was not only infested with huge spiders (think they might be called wolf spiders), but it also had a hornets nest right above my head inside the shelter. It was pretty sketchy, but I stayed the night and made it out unscathed. I have been bit by spiders and have had critters chew on my gear and whatnot. I guess it's all part of it. You get used to quite a bit living the /out/ life.