First there was Mighty World of Marvel and Spider-Man Comics Weekly in 1972. Followed by The Avengers in 1973. Then this title along with Planet of the Apes was the next wave.
Free gift in issue #1 colour poster attached at centrefold adds maybe £5-£10 to value. A complete run minus two issues and the free poster intact in issue #1 went for £132 on eBay UK back in Nov 2009.
Some terrific artwork reprinting US material makes this title very collectible.
Note: some PR issues may have no value. Selected issues in FN, VF or VF/NM may not exist in some titles.