Many resales of the Holley (Sniper) & other aftermarket Fuel Injection Systems

I would surmise that most folks sell these becuase they will not dedicate the time and hours to tune it Properly. Or Lay out the Ca$h to get it tuned on a dyno.

I have had Multiport on my '79 Volare Slant 6 since 2008. For years, every drive to and from work was a tuning session... Same with super cold winter mornings
Once you get it tuned they are nice.

Also a good working knowledge of computers and closed / open loop systems and engineer brain is helpful.

Also you can mistype a number or put a decimal in the wrong place and it can shut the entire system down too. Learning how to save and revert if needed if helpful.