Who uses RADB? [was BGP to doom us all]

You forgot the other one - expense. AFAIK all of the registries have fees
or require you to be a customer. If there is no operational value for me
why would I want to spend the money? I realize most of you work for
companies that consider a million dollars chump change but that is not the
case everywhere. If you can give me a convincing reason to register my
routes in a RADB I will - but at this point I have yet to see it.

There is at least one free best-effort IRR. Also, as you point out, there
are several IRRs which permit customers to register for free. RIPE permits
(even encourages, I believe) its members to register in its db. ARIN may do
the same, as I see they have a db.