NI or Ni200 is Nickel wire
Ti is Titanium wire
these two wires have a special property compared to the Normal Kanthal most coils use.
Both Ni and Ti wire have a predefined measurable change in their resistance as they heat up.
SO one can actually read the resistance of a wire at room temperature then read it again after it was heated and know the temperature the wire is at using some math.,
This is why these two wires are used in TEMPERATURE CONTROL mode
DO not use either Ni or TI in POWER MODE. These wires will oxidize if they are heated too much and you can inhale some nasty stuff.
originally when Temperature Control (TC) only Ni wire was being used
SO all TC devices are programmed for the resistance change of Nickel wire.
Then Ti wore started to become popular. Not many tanks have prebuilt Ti coils, but many people are making their own Ti coils.
Some devices like your now have a Ti and Ni mode. Why? because the amount of resistance change when Ni is heated is different then when Ti is heated. SO its 2 different set of calculations.
Now some have been using Ti coils in Ni mode and setting the tempertaure about 100F lower.
Thjs works to some degree. Its not as good as having a Ti mode with the correct math, but Ti and Ni have similar properties so the 100F differential works out ok.
NEVER USE NI in TI MODE it just doesnt work well and you could damage the coil or inhale nasty stuff
also Stainless steel coils are now being used for TC as well. But only a few mods have the ability to do this (X CUbe 2, Xcube 2 mini,treebox, any dna200 mod, sx mini M class,)
I have no idea if you can cheat and use SS in other modes.
Now is there a difference in performance between TI and NI?
thats a subjective answer.
Some people feel NI has a better taste then Ti
Others feel the opposite.
Sometime sits a choice between the two when you build your own coils. Ni and Ti each have their own unique hardships when building coils, and they each have their own advantages for coil building.
Basically coils are made form 1 of 5 types of common wires. They can be made of a combination of these wires and there are some other wires people experiment with, but these are the basics:
Kanthal - this is the norm for many prebuilt coils - CAN ONLY BE USED IN POWER MODE - Do not use in NI or TI mode
Nickel (Ni or Ni200) can only be used in NI mode
Titanium (TI) Should be used in Ti mode but can work in Ni mode if you lower your temp about 100F
Stainless Steel (SS) Can be used in power mode - if your mod has an SS TC mode you can use this in that mode as well
NiCHrome (Ni80) Only to be use din Power mode
Hopefully this explains enough to help you out