I use the Amazing Mold Putty all the time for the molds in my Etsy shop...It should work for chocolate, especially if you grease the mold up with something, but if the mold is too thick it will be difficult to get it out without breaking the item because you'll need to flex it too much.
I'd suggest putting it in the freezer until it's really set, then take it out and put the chocolate side flat on the counter on a piece of waxed paper. Flex the mold while keeping the chocolate flat against the counter so that you're removing the mold from the chocolate, not the other way around. If the cavity is too deep or the chocolate isn't set it will be more likely to break or stick in the mold, so make sure it's totally set before you try to remove it.
If keeping the piece flat while you remove the mold from it doesn't work, make another mold that's thinner so that it will be more flexible. The AMP can get really stiff when it's thick, and you won't be able to flex it enough to get the piece out without breaking it. It will keep its shape even if you don't make the mold itself really thin, and you'll be able to flex it better to remove the piece if it's thinner.