Nighthawk M6 Pro - problems with T-Mobile or Google Fi?

[rem45]

I'm going to a place in New Hampshire and I checked the 5G coverage map for AT&T. There is no 5G available in that area and same for Verizon. T-Mobile and Google Fi both appear to have good coverage. T-Mobile gets 5G Extended (I read that the speeds for 5G Extended are not that great, but it has good range) and Google Fi gets 5G in that area. Has anyone had any good/bad experience with buying pre-paid SIMs for either and getting them to work with the M6 Pro? I have seen a few people complain about not being able to get SIMs to work with other carriers besides AT&T.

[JT240Z]

Unless the device has been unlocked by AT&T, it will not work with a T-Mobile sim.  Even after it's unlocked, it will still be limited since some bands that T-Mobile uses are not enabled on the MR6500.