The Front Freewheel System and Positron were both intended for cyclists who suffered from what we used to call DAS (Derailleur Anxiety Syndrome). There were a lot of primarily middle aged people who wanted to start cycling in the wake of the boom but were intimidated by what they perceived to be a complex derailleur mechanisms. Both these products were aimed at novice derailleur users and did exactly what they claimed; make derailleur use easier for the beginning cyclist. Think of them as derailleur training bicycles that would many people, who would otherwise not have chosen a derailleur equipped bicycle, used as a stepping stone to true lightweights.
If you don't think that this was a real issue, consider the number of boom era bicycles that are found that have rarely, if ever, been shifted. It's quite common to find chains that mesh only with one cog, because the owners found shifting difficult and the bicycle spent almost its entire life being ridden in a single gear. Had the bicycle been equipped with Positron and FFS, the owner would have shifted more frequently and almost certainly would have gotten more enjoyment out of cycling.
Positron was introduced for the 1976 model year and FFS for 1977. They both survived through at least 1984, which is a respectable lifespan, While they may have appealed to only a niche market, Shimano recognized that market, gave them products that satisfied their needs and converted many into life long cyclists. It could be argued that Shimano was ahead of their time, serving a niche market. Over the years, the cycling market has become increasingly segmented, to the point where the higher end is nothing but a diverse portfolio of niche bicycles. Personally, I don't consider either Positron or FFS to be market failures or poor products.
Last edited by T-Mar; 10-20-19 at 07:05 AM.