Capital ship killer
"Would work as a capital ship killer but there are already plenty of conventional missiles which do a better job by flying under the radar"
Yes but what if your target was 2000 miles away?
The point of this sort of weapon is unlimited range, unpredictable attack vectors and combined with impossible counter measures.
It makes the main weapon of US force projection (the carrier battle group) vulnerable anywhere in the world at any time, whereas today once at sea its largely invulnerable to even saturation attacks.