If you talking about the FAC ones with the cast aluminum receiver (which is what I am assuming you mean by "interesting"), I'd tell you stay away. You can tell because the cast ones because they don't have the groove on the outside length of the receiver, which is where the sliding stock slides into (pic:
http://mwdg3.homestead.com/files/SAR8.jpg).
I have one of these rifles, late model springfield SAR-8 with the cast aluminum receiver (built on FAC / DC Industries receiver). Some people have said on other boards that theirs function flawlessly, but I have had problems with mine (I think the headspace is off, but havn't spent enough time to troubleshoot it). One of their arguements (sales point) on this receiver was that it is stronger than the sheet metal receivers, which in several areas of the receiver it is true, because the aluminum is so darned thick and solid. That arguement falls apart when you look at some of the areas of the receiver which by neccessity of design needs to be compatible with G3 parts inside and outside, are the same thickness or size as the steel receiver, but made of aluminum, so therefore they are actually weeker, and the receiver is only as strong as its weekest point. The trunnion on these is also pinned in, not welded, and the cocking tube is just pressed in. I have read somewhere (on another board) that the pinned connection will loosen up over time or with enough shooting, as the aluminum bearing areas in the receiver fatigue from the pins, causing inaccracy, but can't confirm cause it hasn't happened to me yet.
On my rifle, the grooves cut into the scope rail are out of spec, and you can't put a flapper release on these rifles, the aluminum is so thick that an HK wide forearm will not fit on it, and since the aluminum is softer than steel, the shelf where the lower grip holds onto just gets chewed up, the mag well is too tight, and the finish sucks. Oh yeah, and a headspace problem.
/rant
(sorry)
But like I said, somepeople love theirs.
---->If anybody else on this board has one of these, and has sent it back to Springfield Armory, I would love to hear how it turned out.
My .02, get a rifle built on a JLD receiver.