I've read on here, on the thread "100% instant painless death" some users were discussing possible complications from n and opting to choose other methods.
In fairness, this has to be looked at in the wider context which is that there are only two users who are vehemently anti-N, one of those thinks the Michele Causse passing which is available to watch on YouTube shows signs of serious discomfort, I'd suggest you watch for yourself and decide whether or not this is accurate. The other is a user who has previously mooted the possibility that Dignitas essentially murder their clients, a conclusion he arrived at after the usual painstakingly tedious yet ultimately fruitless research which he routinely undertakes to support his confirmation bias.
I don't think anybody says N is perfect, it doesn't fit the "100% painless instant death" criteria, nothing does, but there's a reason it's favoured by RTD orgs as their method and is propelled so heavily in the PPH. Some users may prefer to order an online hitman or wait for a Sarco machine, but those based in reality would generally prefer an N passing to any other method.