I had my shades made from
Phifertex Vinyl Mesh Almond 54" Fabric which is 70% shade. In broad daylight, from the inside they are transparent enough to operate the boat without removal. From the outside, they provide complete privacy during the day and surprisingly good privacy at night. I'm sure it depends upon the interior lighting level though.
The interior heat load has been greatly reduced, and the A/C works much more efficiently now. It is too early to know, but I'm sure fading of interior fabrics, surfaces etc. will be reduced as well.
The only problem so far is that they do get dirty and require scrubbing a every few weeks to look like new. Also, after a while, dirt streaks appear below each snap that must be scrubbed. All in all, I love them! I will have them on every boat I might own in the future.