It should be noted that claim is not the same as the better-known exclusive economic zone. The continental shelf thing is only for seabed resources, not stuff in the water column. But that's all that the US is claiming, so it is indeed in line with UNCLOS

I'd argue that expanding the zones a bit doesn't incur costs other than updating some maps, as existing radar systems etc were already reaching into the newly claimed areas, undoubtedly.

Am I worried about my country's creeping reach, and have I suddenly realized there's yet another way to slowly encroach on territory? Yes.

E: why the downvotes?