No bothering with the rinse......
Rain Barrel was one of the first in wash fabric softeners. It was invented to address the often frustration of housewives either having to run and catch their washer's rinse cycle, or restart for a second rinse adding softener.
As top loading automatics dominated the American laundry appliance market few had dispensers for FS. This meant as noted above you had to either catch the rinse cycle or restart. Then came these in wash fabric softeners (FAB, Bold and a few other detergents among a few others IIRC came out with 2in1 products as well), but none of them really caught on.
The liquids were cationic based products which do not play really well in wash cycles as they interfere with the nonionic and ionic surfactants that do the cleaning. The powders were often based upon the same Bentonite clay you find in today's offerings including those Purex crystals.
Consumer Reports at the time rated neither offerings very highly. The 2 in 1 detergents didn't perform cleaning functions very well, nor softening. They recommended sticking with two separate products and adding FS where it belonged, in the rinse. Rain Barrel IIRC didn't wow them over as well with the same suggestions.
I remember when Cling Free sheets came out. There were a sort of foam type cloth, not like the gauze things dryer sheets are today. In my stash have some vintage Downy FS sheets and they are made from the same "foam" type material. Being as they are so rare cut one sheet into smaller bits to extend what I've got. Usually use them only for the scent more than softening anyway.
Loved, loved, LOVED pink Stay Puff FS. It was like the other "pink" FS called "Bonnie" something cannot recall the name but the label had a plaid border going with the Scotland theme.
Stay Puff, and "Bonnie" unlike the other blue stuff at the time "Donwy, Final Touch, etc.." was a cationic surfactant based FS IIRC, not waxes, fats, and oils. So you didn't have the build up that caused things to loose absorbency.
Final Touch's claim to fame was that it contained "bluing" to make laundry whiter. In reality it probably contained bluing agents along with a healthy dose of OBAs, something many "blue" fabric softeners then and now do as well. This is why some FS will cause bad staining if they come into contact with fabric while undiluted.
https://www.youtube.com/watch?v=mxHKAlfYjN0