It should be noted that more than a few woodsmen have cobbled together a saw similar to this from an old chain saw chain. Likely where the idea came from. The primary difference is that these will cut in only one direction. The price is right, but you'll have to spend the time putting handles on and all that, then it'll still cut only about half as fast. In a survival situation, a saw is a nice option.
First priority is a pocket saw which can be very useful for a myriad of tasks.
A larger saw, as reviewed here, is something of a luxury, but very handy to have. The less experienced the survivor, the more important such a saw becomes. If you are going to use such a saw, the ability to cut fast is an important criteria and the chain saw style saws are the fasted available, by a large margin. While both of these saws cut smaller diameter wood, in the range of an inch in diameter, the Saber Cut requires a slightly larger diameter to function smoothly than did the Pocket ChainSaw. The Pocket ChainSaw cuts more like a conventional saw and will give a clean cut nearly every time.