Drop-down visors: are they any good?

What are your thoughts on internal drop-down sun visors? Are they worth having?
Debthehog, MCN forums

The only downsides to them are that a few can become loose and rattle inside your helmet or drop down of their own accord (and if we’re honest here, we don’t think they look as cool as a tinted visor). But among our forum members they are really popular. GingerB says: “I wouldn’t be without one, Especially in the UK when the sun keeps going in and out all the bloody time.”
DazLocCy says: I’ve had it for three years and not experienced any problems or ‘rattling’.  If it’s built well then it should be a great addition, it certainly beats having to stop to put shades on every time the sun peaks out from behind the clouds.  If you don’t like it you can normally remove them anyway.”
LEO61 reckons: “I bought the Scorpion Exo 900, with a drop down sun visor. I suffer no rattling, or any other issues for that matter. A really useful piece of kit.”