I went and bought one for $4.85.
It's available with ranch or BBQ sauce, but I went without sauce to get the full flavor of the new grilled chicken.
The multigrain bun offered the same texture as a regular bun, with a spongy softness that I found really nice. It didn't take anything off the table quality-wise unlike some other multigrain or whole-grain buns.
Overall, Chick-fil-A's Grilled Chicken Sandwich was pretty much a marvel in terms of fast food execution and quality, especially how the chicken was cooked. I'm not a fan of the herb portion of the seasoning they went with though.
Nutritional Info - Chick-fil-A Grilled Chicken Sandwich
Calories - 320 (from Fat - 50)
Fat - 5g (Saturated Fat - 1.5g)
Sodium - 800mg
Carbs - 40g (Sugar - 7g)
Protein - 30g