I have to admit that I do not understand the alure of the pistol caliber in a carbine. Mine is a 223 AR. But, my best friend just ordered a Hi-Point (they were on sale) with all the bells and whistles. He ordered a 40 S&W which I consider closer to a 45 ACP than a 9mm. Since he has a CZ in 40 as well as a PT-101 in 40 it would make sense for him. If it was me, I would have bought the 9mm since it will hold more rounds and be faster out the barrel and maybe a little more range.
Me I like 25 grains of gunpowder behind a 60 grain bullet than 5 grains of gunpowder behind a 180 grain bullet. But, that's me.
The nice thing is you can shoot it in an indoor range as well as outside. And close in, I don't think it would be any less effective than an AR. This is his first black gun (finally) even though he has a Mini-14 (Ranch Rifle).
Just my 2 cents.
Si vis pacem, para bellum