What it does is boost the voltage when the turbine is running below cutin.

Cutin of my turbine is at 300rpm. In other words, there is no output from the turbine at 300rpm. Once it passes that speed, it starts charging.

With the S4w booster, cutin is around 140rpm. Not much, but it IS charging. At 300rpm it is producing 1A. It breaks even at around 340 - 350A and 2A. In other words, at this speed there is no increase in output when the booster is connected.

So, what it does and was designed to do is to give some charge in light winds. It probably works best with a turbine like mine which spins very easily in light winds. My other turbine (which is not flying at the moment, but probably will be by tomorrow) takes a lot more wind to start spinning, but still produces around the same once the wind picks up. Since it doesn't do much spinning in light winds, the booster would probably not do much for this turbine.

The only disadvantage I have found to the booster so far is that it produces some RFI on my shortwave (ham) radio. I have to switch it off to copy light stations. (And remember to turn it on again after.) This will naturally be less of an issue for those who do not have ham radio or live in houses where the distance between the booster and antennas and radios can be greater.

You may say that 1A is not much, but an average 1A is still 24Ah per day that I would not be getting without the booster. That's enough to run my Stirling cycle fridge. :)