> I’ve always heard it’s significantly risky to plug power-generation directly into a wall outlet.

Depends on what is generating the power.

Traditional fuel-powered emergency generators are indeed risky, as they are designed to operate on their own. They do not need the grid to be present as they will generate their own sine wave. This means they'll happily feed power outside your house, and nothing is preventing you from getting a giant "bang" when external power is turned on again. For this kind of generators you need a way to XOR the two, usually with a physical interlock turning off the main incoming fuse before the generator fuse can be engaged.

Most solar panels, including those plug-in ones, are designed to operate with a grid present. They don't generate a sine wave, they just sense the incoming wave and "push back". Turn off the external power and they'll stop operating. So no power during an outage, but also no risk of electrocution.

With plug-in sources there's an additional risk, namely that something else on the same fuse can draw power from both the outside grid and from the additional source. The breaker in your mains panel will still trip at (say) 15A, but there's now a second thing supplying current. If that provide an additional 15A, some piece of equipment on that circuit can now draw 30A without tripping any breakers - and its plugs and wiring are not designed for 30A, so they'll catch fire. This has to be avoided by giving the power source its own dedicated hard-wired breaker. Or, in the case of those plug-in PV panels: limit their power to something which is unlikely to cause issues in practice. That 15A wiring isn't going to melt at 16A.

If people are interested, the magic word is "islanding" and the key technology you want which makes this stuff safe to deploy is thus "anti-islanding protection".

If your device discovers it has become an "island", generating power with no real grid (maybe there are two similar panels next door but not a 10GW power grid) it switches off. This is not only safer for you, it's also critical for repair people who might be fixing some overhead line miles away and then a dozen stupid devices inject lethal power onto a circuit their operator has assured them is dead - because from their end it was dead.