Based upon Bluetooth 4/Bluetooth Smart and therefore compatible only with the very latest iPhones, iPads, and iPod touch, Wahoo's new Balance ($100) is a nicely designed digital scale with a wireless weight tracking interface in app form. The scale is topped with a thick piece of glass, and balanced with four pressure-sensitive rubber feet; there's only a single button, and that's to shift between pounds and kilograms for units of measurement.…