I think Nitrogen asphyxiation has a lot of problems. You can’t absolve the terror a person goes through knowing they will die unwillingly. The process can take up to 15 minutes. I’d probably have a panic attack just watching or especially partaking.
People who ordinarily go through nitrogen asphyxiation have the advantage of not knowing they’re dying, because it’s usually by accident or negligence. An inmate can’t possibly share this benefit, unless they’re quite drugged during the process or mentally unfit for execution due to general unawareness. Inmates who get executed in this way live through the entire process fully aware they’re being suffocated, even if Nitrogen suffocation is better than CO2 suffocation.
Also, I owe you a source for this last section that I’m about to provide, so you don’t have to take my word for it. IIRC, if you do not get the nitrogen and oxygen ratios right, the person will experience some symptoms of sickness due to low blood oxygen and will survive barely. The process is a akin to waterboarding IIRC, and has a history, in at least one country, of being used to intentionally inflict that effect as a means of torture. Again, citation needed on my part, and perhaps someone can help me out here find the source.