I forgot to add that the TRE was originally meant to do exactly what it says, remove timing retardation. In gears 1-3, the timing on all FI Suzukis are retarded below 4K rpm, so, especially with aftermarket exhaust systems, you will notice the bike lurching and being otherwise unresponsive around corners. By fooling the bike that it is in 5th gear (originally 6th @ 15K), it runs the higher gear maps and advances the timing. So, for 2001 models, the mod is two-fold.
As to whether or not it hurts ¼-mile times or not is still debated. Some report as much to 1-2 mph differences, either better with it or some better without it. Since the bike runs the 5th gear maps all the time, the fuel and timing will be different. Also, since most launch above 4K, a TRE may not be of any use. If you are not racing, driveability will be greatly improved. If you want the best of both worlds, you can make a switchable TRE simply by using a DPDT-switch or building an active TRE or, better known as Bruce's TRE.