Pocket Wi-Fi had its moment before phones could hold two lines. For most travellers that moment has passed — with a few exceptions.
Price
A pocket Wi-Fi rental in Japan typically costs ¥700–1,200 a day plus a deposit, picked up and returned at the airport — so ¥10,000–17,000 for two weeks. A Roambee 10 GB Japan eSIM: €22.90.
Convenience
An eSIM lives in your phone, installs before you fly and needs no charging. A pocket router is one more device to charge, carry and not lose — and a queue at the airport counter at both ends.
When pocket Wi-Fi wins
Groups of three or more sharing one connection heavily, laptops that need all-day connectivity, or a phone that does not support eSIM. Even then, a 20 GB eSIM with hotspot usually covers a couple of devices.
Hotspot is included
Every Roambee plan allows tethering, so a phone with an eSIM is effectively a pocket router you already own.