The one that I tried out today is the Fiskars Swivel Knife. It fits on your finger and you use it like a pencil. I used a stencil that I made using the cricut and embossed the shape into a piece of fondant using a rolling pin. I then traced the shape with the knife, and applied it to the side of the cake by picking it up and sticking it right to the cake. The fondant was about 1/8" thick, and required no special treatment like the stuff that you put through the cricut.
It took me about three minutes to roll the fondant out, cut the shape and apply it to the cake, so the time wasn't too bad. If I had to do a bunch of these I might start thinking that I'd be better off doing it with the cricut itself, but then once I started rolling it out thin enough, letting it sit long enough, etc. etc. etc. the time plus the aggravation wouldn't save me anything over doing it by hand.
So if you were holding out on getting a cricut, or if you did get one but you're not using it as much as you thought you would, this might be a good technique for you. You can even take the stencils that you cut and emboss larger pieces of fondant with them, (see below) then use those for draping or wrapping a cake. No cutting of fondant required!