Color me unimpressed.
T-Mobile coverage maps show 5G coverage here in San Francisco, but I've yet to get a 5G connection with my Pixel 4a (5G) anywhere in or around San Francisco, not even right next to a claimed 5G tower, even with the necessary R15 SIM.
When I asked at a T-Mobile store what I had to do to get a 5G connection, the answer was "drive to Santa Clara" (over 40 miles away) because "there is no 5G service in San Francisco, only in parts of the South Bay and East Bay."
I filed a complaint with the FCC on the coverage map issue, and got a call in response from the T-Mobile "executive office" with a promise to check with the "network team" and get back to me, but I've not yet gotten that promised call back.