Run away fast.  That stuff is nasty.  I use flaked carnauba wax per a recommendation from Walt Melander of NEI fame.  Available on eBay or Amazon among other places.  I light it after sprinkling some on the melt and let it burn.  If I am lucky, I will have remembered to take down the paired smoke detector that goes off in the garage as well as the shop where I am casting in front of an open door with a fan blowing out.  If I forget about the detector, the family comes running after the one in the attached garage goes off. 

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   I have been using Marvelux for ten years or so and have no problems with it. It works well and produces little smoke which is important to me. I used to use a bit of beeswax but the smoke made it impossible to flux inside without opening windows and using fans, not too practical in cold weather.