1. Metaphysical fertility as opposed to sterility
Does this circle open up a rich prospect of questions with some promise that answers might be found to them and a suggestion as to what the means of discovering the answers might be, or does it close down further discussion or render further questions pointless?
Does the circle promote, justify and facilitate scientific and philosophical inquiry or does it undermine it?
Nihilism, Solipsism and Subjective-Relativism fail this test.
2. Psychological wholesomeness
Does this circle give hope, value, purpose and meaning to your life (or at least allow for the possibility that these things might be real and apply) or does it render your experience and existence void and futile. Pascal's wager applies here, it seems to me.
Nihilism, Solipsism and Existentialism fail this test.
3. Ethical solidity and life-direction
Does this circle give you an indication of what "good" might be and what you ought to be doing and what you ought to avoid - and why; or does it leave you rudderless and directionless? It seems to me that it is better to be moving - even in the wrong direction - than to be stuck paralysed and motionless. If one is motionless one will not discover new things which might help one onwards in one's journey - even if the only thing one discovers is a sign-post pointing you back the way you have come!
Nihilism, Existentialism and Subjective-Relativism fail this test.