it is reliable and peaceful if done correctly, you also need to not get found so 24 hours where nobody is looking for you are very important, you will most likely die before 12 hours but just in case.
getting found is probably the only way you are going to fail, all of the failed attempts that i've read about failed because someone was there and took them to the ER and since this method works by slowly stopping your hearth, doctors can just force it to work very easily.