FWIW I like the STK hand guard a lot, its very very well made, has a heat shield and fits more smoothly and easily than the LHV does. Unfortunately the STK is a lot heavier at 8.3 ounces on my scale (compared to the LHV at 5.9 and the regular poly lower at 4.4 ounces) and it definately feels like it. I wouldn't say it unbalances the weapon when mounted because you know when the adrenaline is pumping during training you tend not to notice these things, but just fooling around the house its noticeable.
The plastic is much tougher than the LHV and tougher than the regular HG polymer from what I can see...it's thicker and feels harder. Not to say the LHV is weak or inferior, just think of the STK as the LHV47 on steriods. It's solid, and you get the immediate impression its intended for heavy use, not looking cute on the range. I kinda feel like you could use it as a hammer if you removed it from the rifle
The STK is very similar to a regular AK lower including a metal reinforced front where the HG retainer secures it and the modern back end where it fits into the receiver. The LHV is all poly and has no metal reinforcements, the rear is also different. The STK is not as overmolded as the LHV where it secures to the receiver and it has fit both my SGL31's and SLR105 smoothly, the LHV is more finicky but does fit all 3. The rails aren't metal but they seem even tougher than the poly body plus they can all be removed including the bottom rail, whereas on the LHV only the two side rails can be removed. I'm not sure why you'd want to remove the bottom rail but you could if you wanted to. Like the LHV it has to be modified to fit an Ultimak, I haven't bothered because I think I will probably sell this down the road. I bought it mainly just to see it first hand and do a little review on it so I didn't want to hack it up just yet.
I dislike the price...to me it's way too high at $99. I think $50 would be much more reasonable but then again its imported and I doubt there is a large market for it over here. I guess you can't do much about that but I still wish it were cheaper.
Overall I'm impressed with it, though I'm not sure how much I'll actually end up using it since the Ultimak covers all my tactical needs at the moment.
STK side
LHV left and STK right
Front STK left and LHV right
Back STK left and LHV right
Top STK left and LHV right
Bottom STK left and LHV right
I don't use this configuration but it's very handy
Z