I've always been under the impression that this and several other similar items worked just fine...
But the problem was not everyone got "a good bottle". Extreme temperatures, over exposure to sunlight, age, etc, etc have been suspected of "killing" the product explaining why not everyone has the positive experience you are documenting here...
As for your test, it doesn't surprise me you never caught the nitrite spike. since your tank has had (approx) equal amounts of Ammonia 'eating' bacteria as it does nitrite 'eating' bacteria, the nitrite was converted to nitrate as fast as it was created...
The reason we typically see nitrite spikes is because of the unbalanced numbers in bacteria during the cycling process...