Do not use on wet snow pal, from about -10 is best.( colder even better!)
Not slippery in use for me atall.
Always go larger mate, you can make up the volume with another pair of socks if you have to.
I have a pair of the usaf issue mukluks. Go for at least 2 sizes larger than you would for regular boots. Even with just the felt liners, you want to make sure that they aren't too tight, or else the blood flow to your toes can be restricted.
As Chris said, these are designed for serious sub zero temperatures, -10 and below really. If you think you are going to be in warmer or mixed conditions, think about getting pac boots instead. Mukluks and damp really do not mix, even the tough military ones.
Hope you are going to put them to good use in proper weather (none of this boring, warm sunshine we have at the moment .)
Best of luck
I've worn mine after i pimped them out (i have got a thread on here somewhere; pimp your mukluks, from a couple of years ago) in sweden and the canadian rockies in December time. Really comfortable and toasty warm. The rubber soles offer really good traction and protection and the removable felt liners are really good quality. The colour is awful, hence my need to dye them. but, all in all, they were an absolute bargain and i would recommend them to anybody.
The medium (for shoes up to size 9 according to ebay seller) british over boots/mukluks fit perfectly over russian valenkis (felt boots) in size 11.
I hope for a really cold winter so I can give this combination a proper test