Well, if you buy the SERT you get the expanded RPM range. The TTS replaces the SERT and thus they can control the RPM and thus the Tach but it is still a NB O2 arrangement or open loop. I still like the WB O2 sensors and the ability for the system to adjust to heat, humidity, altitude, gas and other variables.
I remember when we had chains, kick start, drum brakes, carb's that wouldn't adjust to altitude (the old way). HD knows this but because of EPA stuff they have ( I'll give them the benefit of the doubt) to go with NB O2 sensors to keep the AFR above 14.2 to 14.7. However, the 110 then runs very hot and loses power.
I guess when HD goes to water cooled we'll get much poorer gas mileage but meet the EPA rules. Even the Jap and Euro bikes have issues with heat (reference the Honda Gold Wing and ST1300).
Thus, the aftermarket guys either take over the ECM from HD (TTS or TMAT) or leave it in place and basically trick into working better (Fuel Pak and PC V).
Seems, HD would allow a simple override of the tach but I guess not.