- It's easy to acquire if you know where to look.
- It's relatively cheap compared to other methods (though it's gotten much more expensive over the past few years).
- It's very lethal and reliable if you follow protocol, and more importantly don't get found early or call for help (the majority of failures are caused by these two factors).
- It's legal.
- It's easy to execute (just drink a liquid, similar to nembutal).
- It's logistically and technically easy to set up, unlike things like inert gas or CO (CO in particular can be finicky, while inert gas can be complicated for some).
- You can do it from the comfort of your own bed, which some methods do not allow for.
- It's relatively peaceful compared to other poisons and methods. If you hate nausea or vomiting, as well as tachycardia, the method may not be for you (unless you're willing to tough it out).
- It works quickly (unconsciousness in 15-20 mins, 35-40 mins in the worst case scenario. and death within 40-60 mins, to a few hours in the worst case scenario).
- There appears to be little to no permanent damage if you fail (even for individuals who had 90% or more methemoglobin concentration and died were brought back with little to no issues), though this could be a case of survivorship bias, it's also backed up by medical journal case studies.
I personally classify it as a silver-standard method, with gold-standard methods being guns, inert gas, barbiturates, and fentanyl (if you get lucky and get a high potency batch of pills). But these methods all have issues of access, legality, and technical difficulty, so it's not always an option for everyone.
That's why SN is so popular here. It's a lot easier to just drink a liquid and tough out some general discomfort and illness for ~15-20 minutes than hang yourself, jump off a building, get hit by a train, and whatnot. There's a reason why overdoses and poisonings account for the majority of suicide attempts - it's simply easier to ingest something orally, as your SI is not triggered so strongly like with methods that involve body envelope violations. The only difference is, SN is extremely likely to work, whereas something like ODing on antidepressants is just gonna give you a bad time at the hospital + a psych ward stay. And as already mentioned, it's pretty easy to acquire even today, it's simple to set up, it's relatively cheap (i'm pinching for pennies and I was still able to shell out $150 for a full SN protocol), you can do it wherever you feel is most comfortable, it's easy to execute and pull off, it's by no means the worst method in terms of suffering endured before death, it's very effective, and it appears to be safe to attempt even in the event of failure (it's easily reversed at the hospital).
If you feel like CO is a better method for you, then I'm glad you have a method that is right for you. But for others, SN is the method that is better for them, and there's very good reasons for it, just like CO. Every method has advantages and disadvantages, and VERY few people are lucky enough to get something like Sodium Pentobarbital these days, or put together an inert gas setup, so a totally peaceful and pleasant death is out of the question for many. So it's just a matter of picking your poison (pun/gallows humor unintended).
edit: lmao I didn't fully read your posts before making this, so I didn't see that you asked if combining CO and SN is worth doing. I thought CO was what you thought was better. So to answer: it's not necessary. CO is very effective IF you can get the proper concentration going, and SN will only make the experience less peaceful. And if you're doing SN, CO is just a needless extra step of complication. SN is already very effective on its own, barring you are not found early or call for help, as previously stated.
