it is kinda expensive, and you wont get a big increase in power, . but same with a slip-on....... it will smooth things out, i noticed that in combination with the TPS adjustment my bike is much less prone to jerking at super low RPM's. part throttle response was better as well.
anyway, what it does is eliminate the factory default softened timing maps in the lower gears. basically, to pass noise and emissions tests, suzuki programmed the ECU to pull timing in the lower gears. not a huge amount, but its legit. less horsepower. anyway, the ATRE fools the computer into running optimum timing all the time, in our case the 6th gear unrestricted map.
you can fab up an ATRE for cheap if you are savvy, or buy one off the board members for like 30 bucks. but honestly, i didnt feel that the price was unreasonable given the bonus of a gear indicator, the quality construction, and i just get a hard-on for gadgets