From the quick research I just did, they seem to be a peaceful fish and won't do yours any harm. However, if you can keep one also depends on what your tank looks like. Do you have a sufficient hiding places? Plenty of driftwood? Live plants? Banjo catfish seem to like to blend in with their surroundings and would prefer sand to gravel because of their build. Someone with more experience with these fish would be a better indicator, but I think the guidelines I put out will help you figure out if you can house a banjo catfish in your tank.
Also, I kind of love the way they look! Maybe I'll consider getting one or more in the future.