From Centerfire systems link
$39.99 - MAG TACTICAL SYSTEMS MG-G4 AR-15 STRIPPED LOWER RECEIVER
Interesting, I guess if you wanted the lightest this is one way to help you out.
At 35% weight savings how many ounces would that be?
Is it lighter than the plastic or hybrid lowers?

It is really the ultimate SHTF lower. The real value comes from using it to start fires.

I understand it is as light as a plastic lower, but also have read it is as failure prone. A couple pics of broken ones on the webs

Here

A milspec lower is only like 7-8 oz, so the weight savings was not worth the possible reliability concern.

Reading the thread it looks like the dude was "mortaring" his rifle with the stock not completely collapsed. I think at $40, so long as you're not trying to (what I would consider) abuse your rifle, it's a good deal.

We used quite a few of them as I scored about 300 of them on clearance... when we first opened and lowers were still hard to find.

My experience with them, and there are a LOT of grab bags that we did (70-80) with magnesium lowers, was pretty freaking good. In fact, they had very tight tolerances for the price and I was very happy with how they shot. The only failure that I really know of them has to do with improper mortaring. In fact, it happened with one of our guns even though I warned the customer about it. Otherwise, I have something like 200 guns out there that we did that have magnesium lowers and had a lot of people come back asking for more.