How about a 22K hornet results will be about the same, dies are readily available.
For me the answer is case life of the Hornet, or K Hornet, which is comparatively short. Them thin little necks just don't last as long as Fireball.
I don't personally own one, but my very most bestest ever friend owns a CZ 527 Fireball, and case life is on par, even maybe a bit longer than 5.56.
As mentioned, a fella could form Fireball from GI 5.56, making the cost REALLY attractive over the long run.