I'm not an electrician, but I watched an efixx video on this recently, they explained that if the rcbo tripped and the power remained on the output, it would burn out the coil for the relay.
The thing is that PV inverters stop generating when they lose grid connection, so surely they won't remain supplying power and this not burn out the relay coil???
When I had more solar added last year my CU was replaced, and I doubt very much that a bi-directional RCBO was used.
I will be having the electrician back in a month or two, so I will mention it to him, but it'd be interesting to get your thoughts.