Ultra Boy? No, he was a one-off. He gained his powers through a dose of radiation.

He had all the powers of Superman but, as you say could only use them one at a time.

The power that got him into the Legion though (All Legionnaires had to have at least one super power unique to them) was his Penetra-Vision. It outclassed Superboy, Supergirl and Mon-El in that it gave Ultra Boy the ability to see through practically anything, even lead.