The mt3 should work fine with the spinner and any other "ego" battery out there because it works with the outer threading. Any 510 connection without ego threading will need a 510 to ego adapter.
The ego-t 18650 has ego threading according to the page you linked so it should be compatible without an adapter.
Thanks. I appreciate that insight. Now I'm on the fence again... I'm partially thinking about canceling the order and getting a setup (maybe even still with the MT3's?) and getting a battery setup with replaceable batteries... like 18650 or whatever...
Any suggestions before the evening lands when I want to have the decision finalized?