It's the same. Just point, line up the arrows (or the dot) and shoot.
There's some concern, of course, that the meter may not measure properly with the filter in place. When in doubt, give 1 more stop. It's just too much of a hassle to unscrew and rescrew the filter for every shot.
Of course, the best alternative is an incident light meter. But then, why use an M6 or any metered M?
<a href='http://www.rangefinderforum.com/photopost/showgallery.php?cat=500&ppuser=767'>My Gallery</a>