What year is your bike mate?
Both the Maximus and Power Vision keys work well on the 2019. Pricing is a little more for Maximus. They are a means of unlocking the computer so we can access various settings to tune the bike. My personal preference is Power Vision due to the better data logging on my dyno, but I use both. One has to purchase an unlock key, which is a one off for each bike, and then dyno time. Each brands provide a form of adjustment, so the bike will run as well as it is adjusted. Various "canned" maps are available, but personally I tune each bike. As you are keen to do some work at Heathcote or Whyalla Norrie drags, a tuner can remove the speed limiter and other safety things to improve the general performance.
You don't say what year the bike is , but 103 is twin cam. I would prefer to use a power vision license to tune that bike. If the Black Super tuner is an original one from back in the day, it cam be upgraded to work fine. If it is a later one , chuck it in the bin.
I have just bought a Sport Glide 103 and it came with the black Harley tuner which I believe is very limited and I think the bike runs hot.
Scouser said he had a 103. As they are yet to my knowledge to make a M8 103 I have given him and answer relating to twin cams. I repeat, if it is an early black dongle from back in the day, I can upgrade it to work( same as the orange ones) . If it is a later one throw it in the bin.
Gidday - new to the HD Forum.