Do aquarium bacteria starter in a bottle work?

Snake Oil?

There are a number of starter bacteria products on the market such as API quick start and Seachem Stability. They do work to accelerate the nitrification cycle but bacteria cultures are sensitive, especially to temperature. Depending on how they are transported and stored - the efficacy of such products is easily affected. Bacteria outside a bio-film is also more vulnerable to environmental factors such as harsh chemicals or chlorine.  

A side from bacteria cultures. One can use the old method of using old filter media or mulm from tank to kick start the cycling. This works very well as it probably contains a larger range of microbes that are already suited to your area's water.

​Raising the tank temperature to 28-36 degrees Celsius (82-97f) also speeds up bacteria reproduction. As does having some carbonates in the water.

However, if for some reason you already have livestock in the tank, ammonia toxicity is much lower when the water is acidific (below pH 7), as most of the ammonia exists in ammonium (NH4+) format. So keeping the water acidic actually prevents livestock from being poisoned by ammonia. 

Bacteria does not work below pH 6 ?

One of the remnants of anachronistic aquarium science is the belief that bacteria cannot survive or function in low pH (say <6) environments. Plenty of natural lakes and rivers have pH ranges below 6 and they are definitely not sterile. Scientific studies such as this one show that bacteria nitrification still happens in low pH environments.