Fitbit (One or Zip model) OR new Polar FT4?

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Question: Polar FT4 heartrate monitor (I already have an HrM but this is better) OR... A new Fitbit? And if you say fitbit, is it worth it for the fitbit One or just go with the Zip model?? I know what each one does I'm just trying to make a good decision... I really want both! Haha.. Help a sister out :)