I designed the original Pak-Rifle that Ryan did the review of. That rifle does not have any elevation adjustment, that is the accuracy issue. It will group just fine, but that may be 3" high or low, with no way to compensate, except for using a scope. This issue was not by my design, but rather a restriction imposed by the tight wad manufacture I worked for at the time. It is a very good design, but is not executed well, and they charge way too much for what it is. They changed the name from Pak-rifle to pack-rifle after I left the company uncompensated for my work. They are also operating under a different FFL (federal firearms license) which usually indicates legal issues. Buyer beware.
The PRK, "pack rifle kit" that I currently produce has been reviewed in Petersen Hunting magazine, and builds on all of the lightweight tech from the original. The Ruta Locura PRK uses much higher grade carbon fiber than does the other. The "pak-rifle" is actually quite fragile, the stock can easily break, and the barrel is not as strong as the Ruta Locura PRK. This is merely a function of material choice, not design. You can do pull ups on a PRK, dont even think about it with a pak-rifle. As for delam, I have been building those barrels for 17 years now, and I have never had a failure. The rifled steel liner is the same high quality used by all the big carbon fiber barrel builders.
As mentioned above, the real weight savings is in the barrel. The carbon barrel I build is only 4.5oz. There is some weight to be shaved out of the stock, but not as much as the barrel. The biggest gain WRT the stock, is getting the bulk down. That alone makes a big difference. Also as mentioned above, please keep all mods legal. Barrels can not be shorter than 16", and functioning rifles can not be longer than 26". If the rifle is not in a functioning condition when shorter than 26", you are ok.