Many MVNOs have "unlimited" plans that are definitely not unlimited. If a plan offers 50GB of high-speed data and then throttles the connection to 256kbps, it's a 50GB plan. By contrast, a plan like T-Mobile's Go 5G Plus/Next plans never slow your mobile data.

Other plans like T-Mobile's Go 5G (regular) will be lower priority once you've used 100GB. That lower priority averages 11-15% slower. Most of the time, the network isn't congested and it doesn't matter. You get virtually the same speed as truly unlimited plans. 11-15% slower isn't the same as getting throttled to 256kbps. Of course, it will depend on network conditions. If you're at a fireworks show or a music festival, lower priority might be a lot slower.

There are options if you want truly unlimited mobile data. If you're looking for hotspot, that's harder. T-Mobile does offer its Away Unlimited plan for $160/mo, but that is lower priority - 13-30% slower at the 25th and 75th percentiles. 77-292 Mbps from the 25th to 75th percentiles is pretty decent performance, but if you end up in an area with lots of network congestion, then you're low priority.

"You can pay a flat rate for unlimited use, but after you use 3,000L of water, we will reduce service to your house to 1/10th the normal pressure"

It's fine, you just have to wait 40 minutes between flushes.