NTE is a nice perk when it kicks in, but gearing specifically for it is a little silly. Shihei are what 40 gil each? Enfeebling tools are maybe double that, but you don't cast them nearly as much. So what, at a 20% activation rate (if it even is), that saves you on average like 8-16 gil a cast. Whoopee! I guess if you are going for maximum possible efficiency in your game playing its fine if you put it in on Monomi or Tonko.
Honestly though, you could probably leave that inventory slot open for whatever junk is being dropped by what you are fighting and NPC it and come out about equal. For example a stack of colibri feathers is about 1800 gil to NPC, which is equal to 225 casts of Utsusemi if you assume a 20% activation rate on the belt. Its just not really worth caring about when you do the math.
The point is if you stack it with all your other NTE gear and have Yonin up, you can pretty much free cast ninjutsu, lowering those "OH SHIII*** NO TOOLS" moments. It isn't a massive saving, but check this scenario:
- Elemental Wheel
- 6 hour meripo
Instead of carrying 2 stacks of each (assuming you aren't on Coli's) you only carry one stack and you rarely use a tool. Ninja is a very inventory intensive job, NTE just helps cut that down a little.
It won't dramatically alter your playstyle, but if you can .txt macro in a full NTE set just for your ninjutsu casts, and have it switch back to your TP gear automatically after the casts, which I do, you never have to think about it again and it is there working in the background saving you a small chunk of change per fight. Ninja's toss gil at enemies to fight them, NTE just tosses slightly less of it.
On my NIN at the moment, I have 5 separate NTE's (inc Yonin + Merited NTE) and I have been meriting with it for hours (13 merits this weekend + 16 last week total). I am still on my first Shihei stack (41 left) and have barely even dented my spell tool stacks. I do have the Authenticator for the double inv space (which is a massive improvement and has helped me alot) so I am not too fussed, but as I gave away 9 million gil when I quit last time, I am hurting for money. Any option to save a few pennies here and there is welcome.
Yes you won't save a tonne of gil in the short term, but over a few months, you work out your shihei + other tool costs and it is quite considerable. NTE is great in my honest opinion!
And HI MONKEE!