When the service turns one year old, they should release some service statistics and we will find out.
Unless the numbers are too much to disclose.

But they don't have to release any numbers, since they're not a publicly-traded company. I don't know if they've ever released any kind of financial reports, but I suspect they'd only make their future income/earnings public if they were extremely successful--or they might not, since they'd be telling their competitors something they did "right".
Down with Ledger!!
When I say that they will disclose numbers, it is not in an official context, because as you said they are not obliged to do so.
They must disclose numbers within the marketing scope, to convey the idea that the service is being a success.
Now, whether these numbers are viable or real will be another question. Either way, it allows us to have an idea of greatness, because I also don't see much for them to come up with big numbers - it's better not to disclose anything.