E.g. basic Gmail will be free, but if you want something like Undo Send, etc. then you'll have to pay a monthly fee for it.
And these fees from the various sites will add up quickly.
This isn't at all clear, mostly because every "ad" professional I've talked to IRL is as allergic to real data as some people are to peanuts. What you've quoted is a sales pitch.
Here's a review of all the relevant literature on the topic: https://docs.google.com/presentation/d/1PKHVtO6hgwBJS1vafLyv...
Where a giant group is compared to an extremely tiny group and the differences between them are used to make sweeping generalizations about everyone. When this is the quality to expect, it's just good practice to be skeptical.
Edit: Even if this weren't the case, the enormous spread of estimates when it comes to revenue impact really says it all.