As a toy, kaleidoscopes were fun for a little bit but they never really amounted to much. Depending on the type, they were fun to look through for a moment, and then they just went back in the drawer for me. So I don’t know if it’s worse or better that the Rainbow Peephole makes things cheaper by just being a plastic lens in a bit of cardboard.
I guess comparing it to a kaleidoscope is a bit much, even. It’s really just a diffraction lens and it doesn’t distort things. It makes weird outlines of rainbow colored light around them. They’re still for sale for about a quarter a piece (which almost seems a bit much) but God knows when mine was made by Rainbow Symphony, a 3D glasses (the old kind) company.
The reason for their existence is mostly of course to illustrate a scientific principal to children (while being cheap), and they do accomplish that goal in their chintzy glory.