The ones I know are at least built in a manner you can only insert ungrounded plugs (i.e. use class II devices). Doesn't make them that much better though, trying to run a hairdryer plugged into a US power strip was the first and probably last time I tried to use such an adaptor. I've got plugs for the countries I'm most likely to travel to (French, Italian, UK) and should I decide to go somewhere else I'd try to get plugs beforehand and make up my own extension cord.
