This unit worked perfectly to avoid high charges for international roaming on a recent trip to Holland

This unit worked well but it was slow

T-Mobile 2G speeds aka slow as .....) device as does not work on CDMA (Verizon/Sprint) device.

no matter how good the T-Mobile coverage I only got 2G service

AT&T works well in US...

I recommend T-Mobile because this is the most versatile in that they have service in dozens of different countries.