Just sharing my experience with an add-on fuel controller.
I would be one of the few to run a fuel controller on my ST. I have a Bazzaz ZFI. The reason is that when I first got the bike 4 years / 80,000kays ago I was looking for a solution to the rough fuelling at very slight throttle openings, and the ZFI was the solution posed by my mechanic at the time. The installation of the ZFI involves disabling the O2 sensors to stop the ECU fighting the corrections from the ZFI. My mechanic also put the bike on his Dyno and built a custom map for it. The custom map produced from the dyno for my bike is attached. You'll see that it runs the bike leaner at the high end, but enriches the mixture in the range that us older gentlemen normally operate in.
The result was (a) silky smooth running in the troublesome throttle region, (b) supposedly more mid-range and top-end power (although Im not certain I need or use it), and (c) considerably higher fuel consumption - at least an extra 15% on highway running.
It took me a long time to get there, but the eventual solution was simply to remove the +ve addjustments in the light throttle / highway rpm range. Maybe I wasted my money on the whole ZFI adventure, and in hindsight I'm not sure I'd go there again. But the bike still runs nice and smooth at light throttle, and I now get a 'normal-ish' 20km/l riding solo on the highway vs the 16 that I was previously getting. This will get tested next time I do a long run with another ST - hopefully I will no longer be humiliated by Biggles at the bowser