Bowflex -- yes, that Bowflex -- is expanding its lineup past exercise machines to now include Boost ($50), one of the least expensive activity-tracking accessories we've seen so far. Similar in spirit to Fitbit's Flex and other watch-type devices, it is worn on the wrist, and tracks steps, distance, and calories. It then syncs the data back to an app on your device, using a Bluetooth 4.0 connection. The rechargeable battery lasts up to 11 days, and…
