You don't. That stores whatever type of player you are now (e.g. No Jet Player), then turns you into the "Slow" player, then when you put the weapon away it restores it.
Won't that cause problems if you have mods that change your datablock or two of these weapons at once. (e.g. I use the Mega Gun which turns me slow, then get shot by the horse ray - I turn to a horse, but at full speed! - when I put the gun away, I turn back into the Standard Player, which is odd.)
A better way might be to have alternate datablocks for:
Slow Jets
Slow No Jets - only create and use if No-Jets, Jump-Jet or Leap-Jet player is on
Slow Fuel Jets - only if Fuel Jet is on
Slow Horse - only if Horse or Horse Ray is enabled (horse ray runs the horse script)
and possibly use No-Jet Player for "Slow Quake Player"?
and check these every time your datablock is changed. (e.g. when the Horse Ray hits and you're set to the horse, the script checks and you're still using the Mega Gun, so firstDB is set to the Horse and you are set to Slow Horse until you put it away)
