For whatever reason, in the 1970s, the world of "Movie Viewers" took off, as several manufacturers all rushed to market their own movie viewer that used snap-in cartridges of film loops (similar to the Easy-Show Projectors) so you could watch movies!
Actually, it's possible some of them may have predated the 1970s, like this one...

...which may not be a true "movie viewer" at all (I don't recall the details about this item).


And I don't know if Tru Vue's "Roll-A-Show" was a 1960s item or not! But the things really took off in the 70s...

Kenner, of course, had theirs...

Ideal had their Pocket Flix... Heck, even Fisher-Price had their own movie viewer!
At first, these were all hand-cranked, but eventually, they got motorized...

But by this point, the market was falling off severely, I'd imagine, as it already had for the Easy-Show Projector and the Give-A-Show would follow soon after, as the home video market started to appear, and there wasn't a need for these (or 8mm or Super 8mm movies) any more.
And it's kind of a shame, really... I have fond memories of looking through these movie viewers as a kid in the 1970s.
Jon