I use them with candy clay all the time. I put them in the freezer for a few minutes to harden and tap on the back of the mold to make them fall out. I don't see why this wouldn't work with fondant.
HTH
I have used them with fondant - they work great although it can sometimes be challenging to remove the fondant without bending it out of shape. Better success if you add tylose (or gumpaste) to firm up your fondant; the toughest ones for me were when I used straight MFF because I WANTED the molded items to remain soft (for eating)...but I eventually got thru it.
I haven't tried the freezer method yet but have seen it referenced here, for fondant in molds, not just candy clay.
Give it a try!
Quote by @%username% on %date%
%body%