The KJW and TM also have a crappy hop up design thats why TM is releasing a new version.
The KWA doesn't have a lot of aftermarket parts because it already has great gas inefficiency and nothing breaks routinely in them on propane.
The TM design is one that was designed for Duster. Running propane or Greengas through them will cause to fail eventually.
Some KWA guns do shoot hard but replacement valves are cheap and easy to replace.
Plus you can always pick up a m93r later and use the same mags