They seem to run a number of different but very similar things side by side. There's DxO Filmpack for example, but Nik SilverEfex has its own film presets.
Essentially Nik is for bitmap files, whereas FilmPack, although it can be used standalone or as a plugin with other software, integrates very nicely into PhotoLab to give you a seamless RAW workflow.
You also need to consider that FilmPack is not just about film emulations, it also adds in some very useful stuff for B&W work to PhotoLab, like a channel mixer, highlight, midtone and shadow contrast, creative vignetting, etc. All in a way where you are not constrained to do your RAW conversion first and, if even if you move on to other non-RAW things, you can still go back to the RAW adjustments.
The general guidance seems to be that, if you don't want a completely integrated RAW workflow, go for Nik; otherwise, if you have or want PhotoLab, go for FilmPack. Most of the time I don't know which adjustments are part of PhotoLab and which of FilmPack; all I do know is that I don't have to think about RAW versus the rest
Oh, and don't forget the DeepPRIME noise reduction has to be seen to be believed!
And, no I don't get paid to go on about their stuff like this
