Poor/cheap design
The top doesn't have a good seal which makes it inefficient, also it will eat up the graphite crucible because it will be allowing hot expanding air to escape while sucking cold air into the chamber, which makes it work even more inefficiently. It's not a good design at all, thus the unreal cheap price.
If you use graphite crucibles they will be worn out faster do to the surface area exposed to air while heating
The furnace uses resistance heating, which means there are exposed heating elements/wires all around the inside. This also means you cannot use anything caustic because it will start eating through the wires and eventually cause them to fail. Replacing the would not be easy, nor cheap.
I am sure there are some other issues, these types of furnaces are usually reserved for treating metals, like jewelry, etc or for precious metal clays. I wouldn't use it as a precious metal melt furnace. It's easier to use a torch, or if you are really set on using a melt furnace you can message me and I'll give you the name and contact number of someone that would be willing to sell you one they have recently developed that is closer to the old Kerr types, you might even be able to work out a deal to pay via your refined metals, but that would be between you and him. The other option you have is a propane furnace, you can buy them, buy kits to make small ones, or make a larger one from easy obtainable parts.
Scott
