I agree with Zung and don't have much more to add here.
Apeks does use little plastic tabs to help retain the levers in the air barrels, and while they do kepe the levers frpm popping out, they don't as Zung states, do much to prevent the air barrel from rotating. In that regard I much prefer the far stronger and more secure design of the Scubapro case, even though it does mean the materials used in the lever have to be of higher quality (springier metal and a little heavier construction), and that the case is not reversible.
With that said Scubapro could develop reversible regs for the G250V and S600 series, it would just require a separate case with a left hand inlet that would allow the air barrel to be rotated 180 degrees with the lever on the other side to accomodate the left hand inlet. The dealer cost of a new case for a right hand inlet G250V or S600 is under $10 but the cost of a mould for a new case is probably in the $60,000 range, and with smaller production numbers the unit cost would be higher - but still worthwhile to a G250V or S600 user who wanted a left hand inlet reg.