Both could grow their bodies proportionally to become giants among their peers, granting them tremendous strength. Also, Everet had the power of flight while Allon had a flight ring allowing him to also glide through the air. But the similarities did not end their, as each fell in love with women named Yera and Deborah who could assume more than one form. Each were in protective services, with Gym a member of the Science Police of his era and Keith a member of Federal Bureau of Investigation in his time period.
And each loved blue body suits with red vests and swashbuckler style boots. Showing that some styles are timeless, as is heroism. In fact, while Gym was a denizen of the 30th century, he traveled back to the 20th century more than once, including a time over a thousand years before his birth to aid an ancestor on a battlefield in Europe during World War II. Similarly, over a thousand years from World War II, a teacher was contacted by Keith who left him a note in response to his review of one of Everet's exploits during that conflict.
While both appeared as phantoms during the forays into each other's time on parallel worlds, they were both real flesh and blood men. However, for that lengthy period between his time and that future era he reappeared in, Keith as phantom was the counterbalance for Earth-One's Mon-El, who likewise resided for a thousand years in the Phantom Zone from his native time to that when the Legion cured him and made him a member.