The differences in kilns will be the high temperature that they can
fire to and the interior dimensions. Pottery can sometimes require a
higher firing temp than enameling and Metal Clay requires (if you
are firing porcelain). I recommend a digital controller if you are
firing Metal Clay, it does make things much easier and your results
will be more consistent. For enamel, you need something that will
fire at 1450F - 1650F, for Metal Clay you need a kiln to fire from
1145F-1650F and for pottery you need 1000F-2300F. Most potters use
larger kilns than artists dealing with enamel or Metal Clay. Enamel
can use large or small kilns. Metal Clay tends to use very small
kiln sizes.
Sandra Graves