[NathanKP]

I'd say that the most effective DevRel folks do a bit of all three: marketing, engineering, and product. The marketing aspect has already been discussed in great detail, so I'll address the other two areas.

If you aren't a practitioner of some sort you usually can't speak credibly on the topic of the product. If all I knew was the marketing lines about a product that doesn't build credibility. I maintain my engineering credibility by building at least one non trivial application using my company's products every year. This serves both a marketing purpose and community outreach purpose by serving as a real world open source example for developers to learn from. Often my example app is one of the first open source applications out there demonstrating how to use a new technology, and many people learn from it. This also serves a product purpose by giving me first hand experience with pain points that customers face. It also helps me find places where there are confusing things that need to be better documented, often leading directly to me contributing docs or blog posts about the product to fill those gaps.

Also on the engineering side when I write a public facing blogpost about a new product from AWS, it is always written based on my first hand, personal experience using the product in preview internally. Often in the early days of using a product that hasn't been released yet I find bugs and user experience issues that need to be fixed before it goes live. There is no way I'm going to write an article or do marketing for a broken product that doesn't work when I test it out. So there is a bit of engineering QA in the mix for a dev advocate as well.

On the product angle one of the best ways to get a deep, long lasting credibility with your audience is to listen to them and get their problems fixed. I love being able to go back to folks I've chatted with in the past and say "hey we just released a feature to solve that problem you told me about". Additionally some of my favorite products that I've done marketing for are things that I personally pushed for getting funded and built. The marketing message is so much more genuine and meaningful when its something that you were involved in designing. I don't get any satisfaction from marketing something I don't believe in, but when I get to tell customers about a product that I had a hand in designing and influencing the product direction of, then its a genuine recommendation and I think that comes through to the audience as well.