Sure, the Mira-acid fertilizer will work for the azalea, and spruce, and beech, hornbeam, maples, and any plant not listed as requiring alkaline conditions.
For most of the trees, I would use the acid fertilizer maybe every 3rd or 4th time I applied fertilizer. For your azalea it would be the main fertilizer I'd use. Fertilizers for acid loving plants have no added Calcium and do contain Sulfur, which is a required minor nutrient not included in most fertilizer formulas, because calcium and sulfur salts are not compatible in water soluble fertilizers. So fertilizers for acid loving plants are useful for most general species as a sulfur supplement.
Fertilizer can be a complicated subject. One of these days I'll write that article I have been meaning to write. But no time right now.