HTC makes some really nice but under rated phones such a the HTC One m8 and HTC One m9. One problem with these phones is that the battery is not removable. This isn’t really a problem until your phone hangs either in Android or while booting.
Since the battery is not removable, the only way to do a hard reboot is to hold down the Power button and Up Volume button for up to 15 seconds. This will then reboot the phone in the same way as removing the battery does.