Decided to give it shot. Even if it doesn't work I only lose, like, Rs 100 which is peanuts compared to the price of test kits..
Over the past month I have done quite a number of tests using Nessler's Reagent. Here's my findings so far....
Test samples:
- Tank water-> No detection so far for either of my tanks
Keeping 1 Buenos Aires Tetra in 1 Gallon water-> Ammonia detected after roughly 1 day
Water in fish packet brought from Galiff-> Deep yellow coloration of solution after just 1 drop of the reagent, very high concentration of ammonia. Poor fish

***1 drop of Harpic in 10 ml water-> Precipitation

From the tests it is clear that Nessler's definitely works for higher concentrations of ammonia. As for lower concentrations like 0.2-0.3 ppm, its hard to say. The only way to ascertain that will be by comparing the findings with a test kit or, better, by testing a solution with known concentration of Ammonia.
So, that was my experience with Nessler's Reagent. Has anybody else here tried it ?