Okay, smartwatches are a bit of a tough sell right now, at least until Google shows us its vision for Android Wear early next year. In the meantime, fitness trackers are still a good wearable bet. The Fitbit Flex is on sale at Amazon today for a mere $50, but it won't ship right away.The version on sale is black and comes with both large and small band attachments. The Flex doesn't have a full display, but there are a few LEDs that show your step progress. It also pairs with your phone to sync and give you call alerts, but of course you can't see who's calling on the Fitbit.This device usually costs $70, so $50 is a solid deal. You won't be able to get this device by Christmas, even if you do one-day shipping. Amazon says it'll be in stock on December 30th, but you can order now and get the $50 deal.Source: Amazon