EEE here. I've not looked at these in detail myself as they are illegal in my country. Off the top of my head, the big problem I see is that, since you are injecting power BEHIND the circuit breaker an end-user can overload a circuit.
i.e You have a circuit with max current 16A; clever end-user plugs in 3 x 800W panels into different sockets BUT they are unfortunately on the same circuit; now 26A can be potentially drawn through a single cable IN THE WALL without tripping the breaker. This is a BIG fire hazard.
And you can't wave this away with instructions. It has to be 100% impossible for an end-user to do this.
i.e You have a circuit with max current 16A; clever end-user plugs in 3 x 800W panels into different sockets BUT they are unfortunately on the same circuit; now 26A can be potentially drawn through a single cable IN THE WALL without tripping the breaker. This is a BIG fire hazard.
And you can't wave this away with instructions. It has to be 100% impossible for an end-user to do this.