Yes, this is a valid concern. The key issue is the flash’s trigger/sync voltage. Some older flashes are safe, but others can output very high voltage and may damage a modern camera or trigger.

What to do:

• Check the flash model on a strobe-voltage reference such as the Botzilla list, or measure the trigger voltage yourself.
• Compare that value to your camera’s maximum safe sync voltage from the manual or a reliable reference.
• Be careful with older models that vary by production run. For example, some flashes with the same model name can have very different trigger voltages.

Important: a cheap wireless trigger does not automatically make a high-voltage flash safe. Some triggers may tolerate it, others may not. A trigger is not the same thing as a dedicated voltage-protection device like a Safe Sync.

A rough clue: high-voltage flashes often can still be triggered when charged but switched off, but this is only a hint—not proof. The only dependable answer is to measure the flash or confirm the exact unit from a trusted voltage list.

If you’re unsure, use a proper safe-sync isolator or avoid mounting the flash directly to the camera.