Lots of people here have experience with Nature2, all bad. It will cost you money, more money than it will save EVEN IF it works perfectly and exactly as promised. All it does is kill algae, but DOES NOT SANITIZE YOUR WATER!
Got that? IT DOES NOT SANITIZE YOUR WATER!

Hopefully, by killing one (but not the only) thing that uses up chlorine you don't need to use as much. But the cartridges can run $200/season and THAT buys a h*** of a lot of bleach or liquid chlorine! I pay $19 for a 5 gallon carboy (barrel) of 14% chlorine, about equal to 10 jugs of ultra Chlorox. So the cost of one season's cartridges buys ME the equivalent of over 100 gallons of ultra Bleach. If you pour in one every other day those 100 gallons will last you two summers. The N2 will, at best, cut that in half--25 jugs instead of 50. Do the math and you'll see it's no bargain as you'll STILL have copper and silver in the water. Better off spending that money on a good SWCG, which we KNOW works.