I have a cheaper mechanical plastic case Wittner since 40 years and it never worked with equal beats. One direction was always quicker than the other. And Wittner was always known as the best maker of mechanical metronomes.
My parents (I was a kid when I got it) didn’t believe me that the beats are not regular, but they always have been. I never used it because of that. So a mechanical one can be worse than an electronic one.
I don’t have any such problems with electronic ones or apps and I found enough free ones that work well. The only thing that is worse on electronic metronomes is the sound, but at least one of the selection of sounds is typically useable.
My parents (I was a kid when I got it) didn’t believe me that the beats are not regular, but they always have been. I never used it because of that. So a mechanical one can be worse than an electronic one.
I don’t have any such problems with electronic ones or apps and I found enough free ones that work well. The only thing that is worse on electronic metronomes is the sound, but at least one of the selection of sounds is typically useable.