Ultra Flash is the mask Matt Trakker puts on when he takes the wheel of Rhino, and it does one clear thing: it throws out a flash bright enough to blind opponents for a moment. All three sources we checked agree on that, with the fan wiki saying it temporarily subdues them, Wikipedia calling it a blinding energy blast and Matt-Trakker.com describing a blinding flash.
The cartoon uses it sparingly. The fan wiki lists it in a handful of first-season episodes, starting with The Book of Power and including Highway to Terror, The Currency of Conspiracy, The Chinese Scorpion and Gate of Darkness. In The Star Chariot the fan wiki credits Rhino’s Ultra Bright lights, and not the mask, with chasing V.E.N.O.M. out of the alien ship.
Kenner packed the mask with Rhino in 1985 and again with Matt Trakker and Hondo MacLean in a 1986 two-pack. The wiki adds a production detail from the toy line’s original color guides, which gave the mask a different working name, Freefall. We have not seen the guides ourselves, so that name rests on the wiki alone.