I've used Mint a good bit in 5 of the top 15 cities in the US population-wise. Other than some events like sporting events or concerts its been acceptable for my needs. Honestly its the smaller towns way out there that usually means I get absolutely no service while a larger network like AT&T or Verizon would give acceptable performance.

And yeah, its "throttled". Doing a speed test right now on a Pixel 6a with good 5G signal I'm only getting 11Mbit down/21Mbit up while I'm sure the same phone on T-Mo proper would be getting >50Mbit, probably 100Mbit easy. But for my needs, that doesn't really matter. I'm not trying to stream a non-transcoded Blu-Ray rip from my NAS to my phone while I'm out and about and without WiFi. Usually if I'm without WiFi its because I'm out doing something, and I'm just wanting to look up something on an app like Google Maps or stream music or look up which aisle some product is supposed to be or get an email/IM or something along those lines. Which, 10Mbit is plenty for all of those needs.

Obviously everyone's usage is going to be different. Some people practically live their digital life entirely relying on their cellular connection and are rarely around WiFi, and its worth it for them to pay more for more performance. Different carriers have different amount of coverage and customers in different parts of even the same city. But for a lot of people like me, I'd practically get no difference in my normal experiences whether I paid $15 or $80 in my usage even if that meant my speeds on the go went from 10Mbit to 1000Mbit, except for my bank account being $780 lighter at the end of the year.