You could make it work for pottery. That's a pretty good price for a potters kiln, it most likely cost more than a grand new.
I'll tell you why I don't think it's good for knives (I'm no expert on knife making, but I worked with kilns like this for several years at a ceramics manufacturer): the volume of the kiln is great. I'm assuming you want to heat treat? You'd better be doing a few dozen knives otherwise you're heating an enormous volume of space for no reason. It would take longer to heat and use more energy (notably more). Many pottery kilns have removable rings so you can alter the size but this one has a solid stainless jacket preventing that. The ergonomics are also all wrong, you'll be reaching down into the heat to grab your blades, potentially burning yourself as you lean in or dropping your work.
A direct answer to your question would be yes, you can make it work. BUT I believe it would be a very poor choice.
Do some research on that model, maybe you can flip it and use the money for a purpose built HT oven.
