You can do both (I did an online order for pickup in store) but since it is an older model that they are phasing out, it may not be at every store. Your best bet is to just order it so can definitely get one but if you want one right away, call your local Best Buy to see if they have it in stock.
If I were you, I would just get a Flex 2. It's a bigger improvement over the Flex.
Fitbit - Flex 2 Activity Tracker - Magenta
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