As he was wearing his uniform and armor, he chuckled and said, "I doubt the cloak will be useful in the Umbra World."
The cloak is useful, but it is not infallible. Scouts were still captured even though they possessed a cloaking armor because it required a lot of energy and was short-lived.
Most importantly, it couldn't work on elves because they have a great sense for living things. They can sense a soldier even if that soldier is cloaked.
Even if they couldn't sense living things very well, the forest conditions of the Lignum world meant that soldiers were always stepping on twigs and leaves. That was a dead giveaway of their position.
So the cloak wasn't that useful in the Lignum world. He has an inkling that it won't be useful in the Umbra world either because the strongest race in that world can also sense living things.
This race can sense living things far better than elves. They have a wider range and more accurate perception of living things.
