According to Van Buren lore, the Stealth Boys (reverse engineered from the Hei Gui) were inferior because they were unstable and caused brain damage leading to paranoia and schizophrenia if used for a prolonged time (it was not a gameplay effect, just part of the background lore for the Circle of Steel). Of course, the Hei Gui stealth field could have had a similar effect, just not as widely known (or the Hei Gui helmet could have protected the user).