A lot of molds(I say a lot since I don't know if it is all of them) are made using quick plug of some kind. Myself, I didn't like the feel as I couldn't get them as smooth as I would have liked. And, they carve and sand strangely to me. As for others, I know many people who use them all the time.
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Who needs a 300 or 800, when I have a 294 and a 295!?!?!