i got one of the Joe Satriani metal picks to try out, and i tried another one, but i can't remember what make it was. the "other" one seemed to have rough edges and was just rubbish. the Satriani ones have ronded edges. i found it difficult to play with, although i'm sure perseverance would help. of course, they're very infelxible, and heavy feeling. it's kinda like running with a bag of weights! the smooth edges were nice for slidey effects though, and you can do some interesting things combining picking and sliding. it's a while since i used it, i can't actually remember what difference it made to the sound :oops:
i won't be switching from ordinary picks, but i certainly think it's worth trying them.