When I was teaching keyboards, I always taught diminished seventh, rather than simple diminished chords. They are interchangeable with diminished chords in 99% of musical circumstances, and it means only having to learn *three* chords and changing the root/inversion as appropriate.

Cdim7 = Ebdim7 = F#dim7 = Adim7
C#dim7 = Edim7 = Gdim7 = Bbdim7
Ddim7 = Fdim7 = Abdim7 = Bdim7

How hard can it be to learn *three* chords ???