2 Gold Foil Heatsmiths in my collection now and I still have not used one in battle yet. I just can't see a use for this card. Looking at its stats:
It doesn't seem to get much more useful till maybe level 10. And even then, and effective 8 health and thorns with amplify isn't the most powerful although I suppose for 2 mana, it is quite alright.
Still, why anyone would go to the trouble of getting this to level 10 when there are more useful 2 mana cards is something I am having a little trouble understanding. I also haven't seen many other players use them in battle either so maybe no one really sees a use for them.