Denitrators

I was doing some searching and reading on various aquaria realted stuff
last night and came across these plans for a 'coil denitrator'

http://saltaquarium.about.com/librar...itratornew.htm

As you can see from the domain, it is in the salt water section of
about.com. If you click on the thumbnail pictures of the plans, you can
see each page of the article (I hate the layout of about.com BTW).

Do these things "work?" That is, doesn't the nitrate have to turn into
something?! What is the waste product of the de nitrifying bacteria?
Wouldn't the TDS levels still rise? If so, doesn't this mean water
changes are still vital? If you are the type of person that only
changes water when the things you test for change (rise in nitrates,
nitrites blah blah blah) then I can see this just disguising the need
to do water changes. Am I making any sense?

Of course I would never DREAM of slacking on my water changes (before
MG says something)