Helpful vs. Useful

I don't find that translation so easy. This is the point: Galician word for "useful" and "helpful" is the same. Adding "Mostly" at the before "helpful" doesn't resolve my problem. I need a synonym to complete these translations. Or at least a different wording.

But it is the same thing. Just translate with the same word.

OK, I thought it would be confusing, although these messages are not seen by the same people.