"Invader on my Back" is an original novel. It was later issued in the U.K. as a hardcover by Robert Hale (1968) and the British SFBC (1969). " Saturn" is a reprint of an Avalon hardcover (1967). "David Grinnell" is a pseudonym of then-Ace Books editor Donald A. Wollheim.
Destination: Saturn was quite a fun read, the protagonist was a little annoying though and the humor of it mostly stems from his character, still I enjoyed it. Invader on my back was a little more exciting, maybe worth an extra star, but I wouldnt say that I found much substance in it, it was fun.