I have a dual-voltage hair dryer, but it’s labeled “60hz” — not “50/60hz.” Is it safe to use in “50hz” England? i think, from reading answers here, that it WILL be OK, if I only operate it on LOW.” Does that sound right?
In practice, your hair dryer will be fine.
A hair dryer has two basic elements: a heating element, which does not care about the frequency, and a motorized fan, which depending on the type of motor will either run 16.6% slower than usual (because it's tuned for 60 Hz but will get 50 Hz) or at normal speed (because it doesn't care about the frequency either). In the former case, there's a theoretical risk of overheating if the fan can't remove the heat enough, but this is almost certainly within tolerance and you're likely only going to use it for a few minutes at a time anyway.