Yes, you can cancel your game membership subscription anytime through your in-game Profile under the Account tab. Then, once your current membership subscription expires, it will not automatically renew. You will receive a notification before your membership subscription is set to renew, giving you time to make any changes or cancellations.
Enjoy the game (membership subscription and/or Smashometer) risk-free and get a full refund if canceled within 15 days (including returning the Smashometer within 15 days, if you purchased one).