^^^^Extreme load consistency and subsonic velocity: IMO the difference is marketing to bolster a collector interest like Federal DeepShok and Winchester bismuth loads.
The majority of .22lr supersonic go transonic @ 75 or so yds: Bad things tend to happen in this transition to a heeled bullet/everything else: Conversely Federal did well in the '96 Olympics with their Gold Medal rds--40grn@1250ish. The cases have a sort of voodoo dimple in the head. I couldn't get a group smaller than a nickel @50 with them. Still have a handful somewhere in a baggie.