I recently installed a TFI / DFO module to correct the lousy starting and low speed performance of the stock injection system. Originally, the bike would either not start on the first attemp, or it would start and then stall 10 to 15 seconds later. It also had a bucking / surging condition below 2200 rpm. Now it starts first time every time, and settles into a much smoother idle. The low speed surging is gone.
At this point my bike is bone stock, so the TFI seemed to be the most cost effective way to richen up the mixture. If you only want to improve the driveability of the stock setup, in my opinion the TFI is the best way to go. If you are looking for major torque and HP increases, you may want to look at the Race Tuner or PowerCommander (some of the other folks on this site could provide much better info than me on this).