My pennant fairy was my favorite fish. I had thought that he was a victim of my anemone (he was stung once, then vanished) but I moved my tank this weekend and found him
So the first obvious thing is..they jump.
As to safety with inverts, it could be that when they get large, they might take those opportunities with hermits. They ARE carnivores, so anything unfavorable that they do in terms of food shouldn't surprise us.
I have 2 cigar wrasse right now and have found out that they definitely like their hermits. There isn't much info on these particular fish and I bought them anyway, so my fault, for sure!
The pennant fairy will keep certain undesireable worm populations under control.
They are very social, very pretty and very active.