The film absorbs some Solution A but it can't absorb more liquid when it goes into Solution B so your bottle of solution A gets more and more empty, but not B. On occasion dump out some solutiuon B so both bottles have the same amount in them, and top them off with fresh developer solutions. No need to dump it all and start fresh.
It does give a speed boost with most films, and seems to be formulated to work best with Tri-X. When it first hit the market in the mid 1960s the claim was a speed of 2400 fror Tri-X, but this was soon revised downward to 1600, still a two stop increase in effective film speed. Over the years Tri-X has been "improved" bunches of times so now it has much finer grain than it used to have. This was partially by way of using a thinner emulsion, and the thinner emulsion can't soak up as much Solution A as the older versions of Tri-X, so the Solution A in the emulsion depletes faster. Most people feel that ISO 800 to 1200 is realistic. You need to do your own test! You're the one that's going to print it.
Lastly, it tends to give a slightly flat negative. If you wet print figure on using a contrast filter of 3 instead of 2.
It's cheap to use, no need to check temperature as long as you're someplace close to "average room temperature", and accurate timing isn't required. 3 to 4 minutes is a good range.
