Raymo2u,
The description on the Apex web page says it all. We don't recommend the polymer AEK trigger for the SD at this time because in some cases it causes a what we call a "Fatal Malfunction", which is to say that the trigger gets bound up and will not function. I will not stake the reputation of my company on making an extra buck for a trigger that was not tested thoroughly in a gun someone on the internet say it works in. I added the line about not using the Poly AEK Trigger in the SD on the web page because we have been fielding calls and emails for weeks now claiming that some guy on the internet says it works and that we're holding out on them.
It's true I have installed 2 Poly AEK triggers in SD's that worked as they were. But the other 2 I tested had the trigger bind up. That's a failure rate of 50% and I'd never stake my life on anything near that bad.
The appropriate trigger for the SD will be released soon (within days) at that point, we'll gladly say that we have a polymer trigger for the SD, but in the mean time it's not safe and should not be used.