Please comment on your experience with Plantation shutters. Yes they look great,

I use those shutters- no problem. Happy Listening!

They will obviously reflect sound differently than bare windows. If that is a good or bad thing will depend case by case. Its the acoustics of the room as a whole that matters, not any single part, though any of those might be tweaked as needed to get desired results.

I have blinds on my right wall. If I position them so they are say,  3/4 closed wouldn't the sound waves once it gets reflected off the window glass get diffused on its way out on the back side of the blinds?

Blinds make poor diffusers unfortunately.My former house had a wall of  windows that the speakers fired directly into.What worked is semi sheet curtains on tension rods next to the glass,2"white "egg crate" foam for the next layer,then blinds on the interior side.The curtains next to the glass were for aesthetic purposes only so it didn't appear to be a crack house:)If course no natural light could get through but it looked good and worked like a charm.

Hey grannyring, my room has a window with a plantation shutter on the left wall, right at the first reflection point from the left speaker. My speakers are toed in a fair way. I’ve played around with the position of the shutter but haven’t noticed a difference. As an aside, I recently installed bass traps in the corners behind the speakers and the difference is phenomenal.