Being built right into the phone is a huge advantage! Even if you manage to get a perfect bluetooth connection (which, on Android, is a much bigger ask than many realize), and ignore the fact that you now have another separate device to charge - there's no beating this form factor. Your options are to use a horrible oversized clamshell design (eg [0]) that turns your phone into a tablet, or don't physically attach to your phone at all and end up being a 2nd device / accessory to carry around with you / manage / lose.
