Based on the auto light, it looks like this flash operates in automatic mode. This means that there should have a thyristor at the front of the unit to cutoff the flash once enough light has been detected. I don't see any manual controls (which would be indicated with ratios like 1/2, 1/4, etc), so it does not appear that you can directly control the output of this flash.
I would definitely not put this flash on the hotshoe without first measuring the trigger voltage. To be absolutely safe, I would use a wireless trigger like you said.