We pre-ordered a pocket wifi delivered to our hotel. It came fully charged and has been easy to use. Two of us are sharing it and have had no issues. Works like a champ and battery lasted all day!

Joyce

Japanese SIMs work fine in Android phones (at least European ones) and of course you "don't loose your normal APN settings". In fact I always have APN settings of various countries stored in my APN dropdown list and choose the one that works in the respective country I visit with the respective SIM, it's not rocket science and especially in Japan the instructions provided are super easy to follow.

If you are "technically challenged" of course WI FI is a safer option but not as flexible.