If your undecided between the fasttech ZNA 30 or 50, I would go with the 50 as its only a couple bucks more.
However you mention box mods, and the ZNA is not really a boxmod, its actually a tube with a "sidecar" .
I have a real ZNA 30 and love the form factor, and performance.
Also if you get a fasttech clone House of hybrids has upgrade services available for the clones.