Yes, I agree. Circulated, but good to have. Especially, in a condition matched set (more like a condition progressing set, as the newer coins are in better shape).
I've found about 4 pairs of 1921/21D dimes in junk bins over the years for a bit above spot. Kept the best pair for my Dansco.
Merc's were my first love and the 21's are Royalty. I have the exact same Whitman folder @Garlicus posted, it was the first folder I ever got. Love that "RARE" punchout they put in the 16-D hole