Look for a pyrometer
This is one of the most important things to look in a Kiln for Glass Fusing. A pyrometer is a device that about tells the hotness of the air in the Kiln. This is extremely important as you need to know the temperature of the kiln on a frequent basis so that the temperature of the glass can be examined. If you have no idea of the temperature inside, it would be very difficult for you to work efficiently.
A window in the Kiln is a must as you need to monitor the glass regularly in glass fusing. You must know what is happening inside the kiln so it is necessary for the kiln to have a window on one of the sides.
Although it is not one of the most important things to have in a kiln, it is still very useful. A kiln shelf ensures regular movement of air around the glass that is being fused. It also ensures even temperatures at all times.
Digital control knob
Most of the kilns have a digital control knob. The main reason for having this device is that you can control the artwork from outside and get the results accordingly, as per your design specifications.