The funny thing is that NAM, ToneX, Kemper, they're all wave-shapers that attempt to take a snap shot of the real deal, though none of them can truly replicate the real deal in all of it's facets seeing the real deal has a number of real-time variables happening between speaker/cab/tube power section and it's power supply, all interacting with another set of real-time variables including various environmental and component temperatures, SPL, voltages etc.
Perhaps component modeling could ultimately be the better choice for a stand-alone tube power amp sim, though only Fractal seems to really dive into this area, and they unfortunately refuse to offer stand alone stand-alone tube power amp models to protect their proprietary work, so for now the wave-shapers are probably the best stand-alone tube power amp sims we have? So for me, for real world usage, they do a good enough job until something better comes along.
Adios