I have recently started 2 smallish tanks using JBL Filter start and did full water tests daily for approx 3 weeks. The first tank I added way too many fish to quickly but had no probs - ammonia levels didn't go over 0.5 at any stage - I was impressed with this product.
I then started a 200l tank with JBL filter start this was following the same pattern until a party goer at my house thought it would be funny to feed them some vodka... Killed not only the few fish that were in there but I am pretty sure killed all my good bacteria also as I am getting ammonia, nitrite and nitrates showing now.
I am sold on the JBL product - and would rec to anyone starting a new tank.
Incidentally - the Smart Start is a TLC product