My first reaction upon looking at my collection of cheap hotshoe-mount spirit levels (12 for $12 on Amazon!) was “you sure get what you pay for… they’re all off!”
But then I remembered the parallax effect. Only the center level (which I didn’t do that great a job of centering, but that’s a discussion for another day) is showing level.
Anyhow, these little things are a godsend; not only do they protect the hotshoe mount (they’re rubberized) but they’re super handy when shooting handheld landscapes, urban/architecture and other scenes that can benefit from minimal distortion. Well worth the $1 each.