When I was living in Seattle I found the service to be shockingly bad. I "upgraded" to 5G and my service got substantially worse. I'd often have "full signal 5G" and barely be able to watch videos in Capitol Hill. I worked in SoDo and I found multiple dead zones between the train station and my work (just a few blocks).
For a while I was tweeting at them regularly with screenshots, but got bored of the "DM us so we can resolve this right away" bots and realized I was screaming into the void. I ultimately wound up switching to Verizon.
Interestingly, T-Mobile service was far better in the 3 other major cities I lived in, but it's still pretty embarrassing that their service is so bad right in their own backyard.
I activated a tmobile hotspot for when I spend time in the San Juan Islands, because on at least one island TMo is the only provider.
The service and hotspot were quite reliable.
While at home - a rural area of northern CA, my fiber provider (which is also the backhaul for Verizon - my primary cell provider) went down for a couple days. The TMo hotspot was reliable, performant and served up both the work I needed to do and streaming TV just fine.
$50/mo with no penalty to activate/deactivate made me a fan. Years ago, TMo sucked a lot in the Santa Cruz area.
I live exactly 13 miles away from T-Mobile HQ (one city over) and their service was unusable. I know, I know, anecdotal. But funny!