Very collectible especially for the early Silver Age Marvel reprints like Avengers #4 (1st Captain America) in #55.
See also the Spellbound (1st Series) title.
Mystic #40 is a big one - reprints the 1st appearance of Groot from Tales to Astonish #13. Tough to find in any condition!
Also #55 which reprints the 1st appearance of Captain America in the Silver Age. Only 3 recorded copies! I have one which is a CGC 7.0 the Highest Graded. And with white pages too.....
Sep 2021: I sold the 7.0 for a very healthy £995.00
Note: some PR issues may have no value. Selected issues in FN, VF or VF/NM may not exist in some titles.