Buying 1 Mibps means you can use up to 1Mibps. Paying $/GiB means you can use 100s of Gibps for a split second and only pay the $/GiB fee.
In the past i did a TCO comparison for a large spikey workload where the $/GiB cost even at list was cheaper than allocating enough bandwidth for peak events.
At small scale the $/Mibps likely comes out cheaper, but for any large company sitting on 100s of Gibps of excess capacity for an event that occurs once or twice a year, or a few hours per day is very costly and might eat up savings from p99/p95th billing.
In the past i did a TCO comparison for a large spikey workload where the $/GiB cost even at list was cheaper than allocating enough bandwidth for peak events.
At small scale the $/Mibps likely comes out cheaper, but for any large company sitting on 100s of Gibps of excess capacity for an event that occurs once or twice a year, or a few hours per day is very costly and might eat up savings from p99/p95th billing.