Yes, SN has been painful for many people, including me, but remember that we're all individuals and our bodies react to and tolerate things differently.
It's not certain to be painful for you and certainly not unbearably painful for the majority of people, even if there is some pain as a result of SN ingestion.
It's a relatively peaceful method compared to the rest.
Even if there is pain, it is easily manageable and compared to most other methods this pain could even be negligible if you are proactive and you prevent the pain prior to your attempt by taking painkillers (which is part of the SN protocols anyways), and to prevent the possible stomach pain (and nausea, but that's unrelated) you should take an antacid.
I'm not sure how this works exactly, so I apologize if this is wrong, but SN and stomach acid react and this forms nitrous acid and this causes irritation of the stomach lining, pain and discomfort, nausea and vomiting, or gastrointestinal distress. The severity of these symptoms relies on the individual's tolerance and the concentration of this acid in the stomach.
By taking an antacid you essentially neutralize the acid in your stomach, and what remains is a mixture of salt and water, so this reaction is impossible to occur and therefore the pain is prevented.
To prevent the possible throat pain after drinking SN, you can use a throat numbing spray before you drink the SN.
Taking painkillers is helpful with a possible headache too, which is included in the protocols.
Although not required for this method but strongly recommended, benzodiazepines or any sedative for that matter would likely make you ignore the pain as you're sedated.
Assuming you have these things, there should be nothing to worry about in terms of pain.
This is not the perfect method though, even with all of this medicine to make the experience as peaceful as possible. I wish such a method existed.