Mi experience with that kind of saws goes as follows:
- I was gifted a wire saw that I carried for a long time before having the chance to use it. When I did, it snapped in half after a few minutes of use and while it lasted, I didn't feel it was cutting much.
- Soon after that (but still many maaaaaaaaaaaaany years ago) I bought a pocke chainsaw (called precisely Supreme Pocket Chainsaw). Used it a few times and it worked really well to be honest. After that, I haven't used it much.
The problem with these saws is that you need both hands to use it, while a foldable saw allows you to grab the wood with one hand and saw with the other one.
Another issue is that the natural and more comfortable way to cut lumber in the ground is to wrap the chain from under the piece of wood, stand with one leg on each side of the log/branch and pull straight up with both hands. The problem is that as you progress through the cut, the branch tends to fold down pinching the chainsaw (gets stuck). Yo need to prop the wood onto something so it folds UP away from the cut instead of down.
With a foldable saw you will approach the cut from the top and don't have this problem.
The advantage of these saws is that they don't take much space in a backpack. Weight wise, I don't think there is much of a difference because they are heavy! (it is a chain after all).
Mikel