eros was my first SSR and i can tell you that she is kinda underrated. That barrier is quite good actually , especially coupled with other defensive boosts (think jeanne's skill). She can pretty much negate an overdrive aoe with it and jeane's skill on anything that is not a ragnarok boss. (or reduce the damage considerably to the point it's not threatening by itself)

Personally , i find it really usefull , but then again , most others don't rate her that high.