Perhaps it comes down to how much risk you think you can afford to take. If you're comfortable with one month, or two months, or whatever, and believe that nothing will shake your INR stability during that interval between tests, hey, it's YOUR life.
If you trust your doctor to stay on top of current research about testing intervals, self-testing, and the use of FDA approved meters, hey, it's YOUR life.
If you'd rather trust these things to others - and not worry about examining current thought about INR testing and management -- well, again, it's YOUR life.
For myself - I'm comfortable with more frequent testing, even if a 'clinic' tells me once a month is fine. I'm comfortable with self-testing, even if my 'clinic' is against it, and even though I'm not sure I can trust my current meter. I know that if something happens -- it's on me. It may be hard to blame a doctor or clinic because, hey, you CHOSE them and you CHOSE to stay with them
For me, weekly testing (when I've got enough strips), occasional looks at new literature on the subject, and fairly careful self-management seem to work fine. I'm comfortable with my choice (but, as noted, not necessarily with the technology that my meter uses).
You can choose to give total faith in your doctor. You can trust your life to your doctor. I just hope that your doctor is on top of recent thought, and not living with what she learned a decade ago about anticoagulation and recommended testing frequencies.