GuiWoo M2 Heart Rate Smart Wristbands Band Smart Bracelet Bluetooth 4.0 Smartband with Sleep Monitor worth to buy? Thanks for it if those of you who have purchased GuiWoo M2 Heart Rate Smart Wristbands Band Smart Bracelet Bluetooth 4.0 Smartband with Sleep Monitor could share about what you think of the product. I would love any extra info, as it is quite pricey as $21.99 and I just want to know it is good before paying for it.