There are several brands and some even recommend by retailers of those products for that use.
B-U-T, been there done that.
A highly recommended one is NuShield DayVue. All sorts of glowing reports about how well they work.
Well I got one for one of my Humminbird 1198c SI units for testing. I put it on the unit I use at the bow.
What it did in function is make my screen a mirror. I had the pleasure of watching myself fish for 1/2 day, LOL
Seeing what the unit was displaying was reduced due to the reflections.
I waited until mid day to get the full affect of its capabilities and took a picture of the two units beside each other with the displays at the same angle. After I took that picture, I removed (comes off easily with no residue) that wonderful failure and later threw it in the trash can at the ramp.
What is does is defeat the anti-glare coating on the screen and it adds another layer that physically darkens the display.
The benefit of it is you don't get water spots or finger prints on the unit screen ( it covers the screen-DUH )
My advice is to carry some Windex Multi-surface with Vinegar and a mico-fiber cloth and clean the display as needed.
This is the picture; the unit on the left has the DayVue---
See the nice blue sky and my orange shirt on the left one?