The only downside I saw is that you have to aerate the effluent before it goes into your tank since it will have the O2 removed in the process. The drip rate is the most important thing. Make sure you follow the directions to the tee if it is a Midwest Aquatics DeNitrator. They have really good instructions and also a forum if you run into any issues. The guys at midwest are extremely helpful. The tubing they send with the unit was 10 feet and not long enough from my setup (not typical) and they sent me more at no charge.
Anyway make sure you start the drip as they say, slow like 1 drip per second then 3 daysw later 3 drips per second. If it starts to smell like sulfurthe drip needsw to be turned up.
Other then that once you have it adjusted properly it's a breeze after that with virtually no maintenance and will take your nitrates down for sure, mine did. In less then a month I went from 80ppm to <5.