Just curious, maybe someone there could answer?
My impression was that RedGate took it over for free, with an undertaking that you would not restrict access to it in the future. The product and community were already built. If this is the case the starting to charge is in really bad faith, in my opinion.
Either way, you should demonstrate you integrity by open-sourcing the code at the point where you took it over (or offering that version for free indefinitely); then I think it is fair to recoup your dev and support costs since then.