Using PIN instead of a password for encryption on Galaxy S5
You can choose a password that exists of numbers only. I've done that with Jellybean, and was annoyed when starting up the phone, and not having the number pad. It worked with Jelly Bean, and I hope it works with KitKat as well. 

Only thing I would prefer is to have a password for startup, complex with letters and numbers, and a PIN for unlocking the phone. That is possible as well I've been told, but you need to root the thing for this to work.