I would suggest you to think again.

As a previous T-Mobile Hotspot customer (still an active T-Mobile customer), my Hotspot experience was far from acceptable. T-Mobile's data coverage is not the issue. Instead, my problem sought to be related to the WiFi devices.

I used 2 different devices (ZTE and Alcatel) with T-Mobile Hotspot. Both are T-Mobile certified (i.e. branded). A side-to-side speed test comparison with my cellphone (not T-Mobile certified) revealed my cellphone data speed, on mobile tethering, was significantly faster than Hotspot. Specifically, I used a iPhone without active service and connected my cellphone and Hotspot respectively. And I used Ookla App to run speed test on the iPhone. The App reported my cellphone data speed as 14Mbps and the Hotspot as 2-3 Mbps at max.

I talked to T-Mobile, which T-Mobile acknowledged the issue without offering the solution. Given that I have more than enough data quota for tethering, I did not bother the problem and cancelled the Hotspot instead.

You may say this was my own problem or else. Bottom line is while I still satisfy T-Mobile service, I would hesitate to use their Hotspot device for the Mobile Hotspot service.

Note - I made the device switch (from ZTE to Alcatel) because of the same speed issue.