Nothing. I'd buy one as a cheap knock about big bore. Probably will one day (or a CZ).

I like a longer tube to get the muzzle blast a bit furthur away. I don't like recoil and I see muzzle blast as adding to perceived recoil. I also like a slightly muzzle heavy rifle so I would check the balance.

I believe the .375H&H Zastavas have had the actions 'opened up' if that concerns you. The .458 is on an untouched standard length action.