Angle limitations lead the list. The experiment tested the cloak with light hitting at a 45 degree angle, and works effectively only within a 6-degree range of angles. Kante said his team is working on ways to expand that. His study states that the math behind the effectiveness of this experiment indicates a “large range” of angles should be possible.

Also, Kante said the technology does not allow for a cloak that can hide an object from both visual and radar detection; a given cloak will only work for a fairly narrow range of wavelengths.

Source: Pentagon intrigued by breakthrough in cloaking technology

But it’s better than the RAM they have now and it’s 10 times thinner. So maybe it covers enough wavelengths to foil current radar, because the current version of stealth is unfortunately quite visible.