I'd say its then more YMMV rather than a blanket "does not live up to the promises".
I can routinely go around most of the metro area on any given day and get hundreds of megabits of throughput back home at <10ms latency on a plan that's costing me ~$30/mo on a device that cost less than $400. I can be in a crowded sports arena and on my regular cellular internet and still manage to pull >50Mbit down despite the crowd. Several years ago, I'd be lucky to even get SMS/MMS out quickly and reliably.