Depends on electrical code which depends on, most of all, your standard plugs. In Germany Schuko is deemed non-optimal, but acceptable, for up to 800W.
...no issues regarding exposed prongs, if the inverter doesn't see AC to sync to it doesn't output anything. It's not a dumb spinny magnet generator we're talking about here.
Most people don't have an outlet on their balcony, though, and weather-proofing the thing is an issue in any case so while you're at it you can just as well put in a proper Wieland outlet. 20 bucks or so, the expensive part will be the electrician not the outlet.