The good thing about this device is that it works with the new 600 MHz (Band 71) Extended Range LTE that TMobile has been rolling out in rural areas. That band works twice as far away from the towers. I already have TMobile so I don't, technically, qualify for this trial. Using this band would be the main reason for me to upgrade my phone.
Currently, the only place I have been where others could get signal but I couldn't is at Jamie's van build party on Shea road, south of Parker, AZ, due to the mountains. But there are other areas south of Parker, AZ that are miles from Parker where I get great signal, even without this new band.
I think the main reason for TMobile to make this offer is to get people to see the benefits of this new band.