You're right, they weren't as common as the bagged models. Mainly because back then the companies thought that bagless was a joke, especially when they realized that they were messy to empty and the filters were more expensive to replace than bags but people started to like them better. These weren't the first bagless vacuums that Kenmore sold, the Built-In Vacuum systems were the first. And yes these were one of the first Progressive models that were introduced, they were sold commonly as blue, purple, red, black, etc.
Just like the bagged versions, these were awesome vacuums, In my opinion it's one of the best Kenmores that they've ever sold. For a bagless upright, I think it's perhaps the best one that I've ever used. I know the bagged versions are better and of course I also prefer the bagged versions better as well but I wouldn't mind cleaning the filters if I only used it once every while like a couple months or so but not if I used it every week. You can now buy generic filters for this that filters just as well as the genuine filters and now wash them as well but for half the price off.