Nistune is not an emulator in the true sense.
Yes it does realtime but you are limited to what has been defined in the tables and what areas of the ROM is allowed to be edited.
As I understand it, what the boys at nistune have done is to patch the original ROM for each vehicle/ECU this enables read and write as opposed to read only via the consult stream. This was a continuation of the work done years ago on the old ECCS.Hydbrika forum and was done using NVram originally on some single chip 8 bit ecu. These ecus usually have the Read/Write header as a separate 4 pin header near the socketed ROM.
You cant load any bin with Nistune in its entirety like with Calumsult, ostrich or even NEMU. And you need their special programmer just to load whatever bin you want. It even means that if you were to discover some new area of the ROM, you couldn't just edit it as you wished (realtime), a simple thing like fan control temps hadn't been implemented although that information was known years ago. Furthermore, Nistune doesn't have a board compatible with the SRxxVE ecus and so would not be in their interest to have a Patched file for it.
If you are looking to spend in the region of $550 and you don't intend to use the CVT transmission, than get NEMU and forget about the rest. Everything is tuneable at any time, you can convert to speed density, you can use Coil on Plug if u have the S13 SR20DET ECU. It really is the best option for the money and documentation and support is readily available.
If you want to get the best out of NEMU then first decide if you want to run COP or to use a distributor. Then either source for yourself the required ECU or order the NEMU and the ECU of your choice from JKTuning. Tell him your current setup and he will load a base tune to get you started, then tune, or have it tuned as you wish, he offers remote tuning services as well.
Pay particular attention to the supported ECU's section near the bottom of the page:
NismoTronicSA Package, NismoTronic - Nissan ECU Tuning
NEMU will run on other ECU's that have the 40 pin header but you will not be able to utilize all the features because of the way the outputs are ECU specific for their ROM, for the best experience, get one of the "right" ecus.