There are ways to somewhat fix it for circuits with a single use.

Fixing the same example: A 16A breaker for the solar feed in, a single 16A breaker for all the consuming appliances on that circuit. And another 16A breaker on the feed in for that circuit is an example that is sometimes used in the Netherlands to add a feed in to an existing circuit with a single outlet connected to it. Meant for washingmachines for instance.

This ensures that the circuit on all circumstances has a maximum current of 16A flowing over any wire by also measuring the outgoing current of both feed in circuits. But if you have multiple outlets you'd still need to stiol measure at a single place or use low enough breakers per outlet that the total stays below the 16A. Which the UK might have if I recall correctly.

Then again this is not a normal setup and requires change in the electric circuit of the home. Which most consumers won't even realize. Like I said, if everyone keeps to the fine print this thing probably has and limits the extra plug-in solar panels to 1 per circuit, it's unlikely to actually cause issues because of overdimensioning of the wires. And the safety margin built in which is likely how they have gotten approval. But ignoring or not reading that text and plugging multiple in on the same circuit can and will cause a fire hazard with heavy consumers on the same circuit.