hi,
And that can be used to generate true random number generation

No if you mean numbers obtained with LD A,R command. It is not true because Refresh register is simple counter which contents is incremented after each M1 cycle. And so there is possibility of situation when not all "random" numbers may be obtained.
Indeed, if program contains some kind of wait loop based on external event (for example, push button) then such random generation may be used. But for strong random generation I preffer to use shift loopback register.

Regards,
Oleg