Self answers should be allowed.
However, a self answer must also have a good question. The question must be on topic and of decent quality. When the question is written, it needs to be able to stand on it's own - without your answer. If the community would allow the question without the answer, then there is no reason to get rid of the question.
In the event that you are asking a question to promote a product you are personally involved with (ie. the manufacturer is your employer, it's your piece of hardware, you receive royalties from each sale, etc.), this must be disclosed. The difference between Hardware Recommendations and other sites on the network, is that a self-answer can very easily look like spam. Spam is bad and should be whacked with every giant stick this community and it's leaders have.
I've noticed, in my travels around Stack Exchange, that self answers tend to be judged much more critically. Be aware of this phenomena. If you can provide a high quality question and answer, then go for it. If you can not, the community is here to explain (via comments, down votes, and close votes) that this particular content is not appropriate.
Finally, a self answer should not be the end of a particular Q&A post. You may have a great question and answer, but the community may have something even better. It's worth remembering that, even on self answers, other answers are encouraged.