Yup. Worst case scenario is indeed mixing generation and load on the same circuit. And you have to assume that some number of people will manage to do that and create a fire hazard. To connect it safely, you need to know the circuit layouts and the rating of the cables. This is not something solvable with a safety sticker and safety instructions. A huge amount of effort has gone into making domestic electrical installs as inherently safe as possible and these panels are a back door to that.

Don't get me wrong, I think they're a spectacular idea, especially for renters. But you'd need an electrician to check the circuit and maybe even have a special balcony-solar-plug to prevent people plugging in too many panels in the wrong locations.

Quick edit: Random idea. I guess if the panel could communicate with the RCBO it's connected to and that RCBO can dynamically alter it's trip current could also solve it. But again, that's an electrician call and new thing installed.