I usually have a soft spot in my heart for gadgets, but I don't see how this is much easier than doing a standard test. You have to do a "null" test, and then another with reagent added, to get a result that isn't accurate enough for reefs. Is it cheaper per test than the other options? I could see some advantages if it was cheaper than other tests. I run a phos-ban reactor, so I usually test 0 for phos. When I test higher than 0, I know that it is time to swap out my phos-ban. So, really all I would need would be a positive result.