My immediate reaction is to doubt you need it, as Mihai says. Taking good care of the tank(water changes, no over-feeding, no over-stocking), good quantities of live rock and a sand bed should do the job for you.
I'd be interested to see feedback on this product on sites other than the manufacturer's.
Word on the street is denitrators are finicky beasts and they need maintenance. If you really want one, they are very cheap to build yourself.
When I looked into them I decided they were too tricky to make work well all the time.
I did install a remote sand bed for extra denitrification though.