these fish are aggressive, but it is confind, in most case to just chasing other fish. they are said to be compatible with most tropical communitys, seems best only to get one though to keep the problems down. tetras are said to be fine companions for this fish.
Yes, they'll eat small tetras. They grow to 6-7" (note that they get larger than the popular, but mroe aggressive, RTBS) so, like with most fish, they'll what they can get into their mouths. Couple this with their territoriality and chasing behaviour and they don't make the best tankmates for very small peaceful fish like neons (larger tetras are ok though). They also are best kept away from slow-moving species that may panic when chased or which could be bullied and nipped.
edit: The link Andy posted isn't the right one (unless it was on purpose for some reason? I didn't read all the sword comments through) so here's the right one: http/www.fishforums.net/index.php?showtopic=41902
i dont think he will cause a problem i have a red tailed shark in my tank and some glowlight tetras and he hasnt taken a bite out of them and they are about the same size as neon tetras. id jsut watch out, heel be fine if hes 1-4" but more he could eat 1...