I am curious about these stocks as well.
The Safety Harbor item looks very sturdy with the round extenders, but it seems very wide at the rear...and requires trimming off the tab at the left rear corner of the receiver with a dremel.
The Manticore item is much slimmer at the rear and follows the Scorpion's receiver shape better, however many of the PWD stocks with flat extenders (like the Manticore) get wiggly and loose with use over time.
I have a Maxim PDW on an AR (which has round extenders) and it is awesome. I sure wish somebody would do a "hands-on"review of these two Scorpion PDW stocks.