What changes the cages answer
Check spacing for the smallest bird that will use the cage. If the head can fit through, the spacing is unsafe even if the cage is large and attractive.
Small birds need tighter spacing
Budgies, finches, canaries, and other small birds need narrow spacing. A cage made for a larger parrot can be dangerous for a small bird.
Large birds need strength too
For larger parrots, spacing still matters, but bar strength, welds, locks, and finish also matter because strong beaks test weak cages.
Check every opening
Measure side bars, door gaps, feeder doors, play-top gaps, and any bent or decorative sections. Birds find odd openings quickly.
When unsure
Choose smaller safe spacing for the bird's size or ask an avian vet, rescue, or experienced keeper before buying.