Yeah I'm referring to fullhop forward airs. They're relatively safe as long as they're well spaced unless against Marth or some of the other long range cast. Our fair is the same distance as Sheik's fair but with a larger disjoint.
On shield it's unsafe though, the purpose of fullhop fair is to get people to come after us while they believe they have a neutral advantage, fullhop fair well spaced is actually quite difficult to intercept by most of the cast unless they come in directly underneath or behind us. Fortunately most of the cast aren't quite quick enough to do that. I wouldn't do it against a Fox though unless retreating at the same time to stop him getting under/behind.
Cosmic was using this occasionally in his most recent win in a couple of matchups, so I'd recommend watching his videos for an idea.