Yeah, it only matters with things like electric shavers (although those are all battery operated now... so it actually doesn't matter!), vacuum cleaners, etc. I know if you plug a 120v appliance into 230v it might kill it, but I guess if you plug a 230v appliance into 120v it just won't turn on or will run slower.
I've used that type you see on the left there. They're awful and dangerous.
It's better to bring an adapter specifically made for the plug you have and the sockets where you're headed.
When flat They're mostly fine, but those "universal" ones have so little grip in them to cater to all plug types, that when wall mounted, the plug usually is left hanging half-inserted, exposing the live conductors.
They also allow you to plug in a grounded Schuko Plug (Its the german one) without connecting the earth, cant get much more dangerous than that.
I think the french plug also can be plugged in but it doesnt connect the earth either.
Universal sockets are the norm in many places now. I have every outlet with universal. They grip stronger than a standard American outlet and have tamper resistance. But like any receptical they wear out and are only good for so many insertions. If you use G type plugs they seemingly last forever.