Pro and Con of multiple heaters in one tank

[Reefmaster]

hey all.
i recently had a 300W fail (off position) and am now in the market for a new one. i run 3 heaters and can't say enough about doing so. i would pay cash/trade for w.h.y. if anyone is looking to replace a big 'un with a smaller unit. actually, i also have a 50W i think that is 1.5yrs old i would trade if anyone wanted. (moderators, i know, not the trading post but fits with the discussion...)
shane