Earlier quoted context omitted.
That really is the worst possible way to put it. Why not express it in nanobytes? PB is a unit everyone is more familiar with than MGB.
*M GB M is well-known in headlines as million. A GB is something people appreciate the size of, TB not as much, and PB is definitely not in most people's vocab.
Nobody measures things in megagigabytes.
To be truly pedantic, "M" can also mean "mille" or thousand if you're talking about things like CPM. Mixing units like this introduces needless confusion when there's already a SI unit for the job: P.