Has anyone tried either Mosto Italiano or Mosti Mondiale sterile must kits?
I`m thinking of trying one for my next batch

Yes : The kits are flash pasturized and sufated to about 150 ppm.
Source of juice is mostly California or Europe (usually Italy, if not
otherwise
stated.)
I used last year the Mosti's Nero d' Avola.
Good quality about 95% of stated juice with 5% or so added
concentrate (to give better colour/flavour).

Ferment just like Fresh juice except will not accept Malolatic as
Sufites to high (unless you wait a year or so then try the MLF )..

These are not Wine kits so require a bit more experiance to use.

I hope this helps.