First, not all visors are created equal. Some block more vision when in the drops than others. My old one was barely noticeable to me, my new one is much more noticeable.
I wear a visor on the trail. It helps me mainly in two ways there. Lots of movement between sun and shade, low sun angles, I like a bit more shade for my eyes in a consistent way. It is marginally easier to see INTO shade from sun. Second, it adds a bit of face protection from dangling vegetation when I have to duck through stuff hanging over the trail. Which I do, given I ride some things that are rarely ridden by others.
I'll wear on on the road but NOT when 1) I am riding in a group, or 2) on a very windy day when I will be not just in the drops, but low in the drops keeping my head down as much as possible. It's not so much I wear it on the road, I just don't bother to take it off unless I think it would cause issues.
I see no reason not to get one, and try it. Worse case, you take the visor off and never use it again.
Or try a cycling cap if you prefer, since you can pop the brim up and down. But that's going to make things a bit warmer for you. More on the trail when speeds are slower, less so on the road at higher speeds.
