I was told the same for pool care by the store and after finding the form and thinking about it I ended up ditching the N2 system. If you are in for a read about it you can take a gander here.
http://www.poolforum.com/pf2/showthread.php?t=405
I was out about $80 to $90 a month on chem and if I used the N2 about $110 a year for the N2 before finding the forum. Last month I spent $29 on chems for the pool. Most pool stores are out to dig deep in to YOUR pockets and sell you magical products. I was pool stored for $425 when I bought my pool. Listen to the pros here they know what they are talking about. They will save you money and give you great advice to have great water.
Waterbear as useual I dont include you in the above statement.
Steve