Ben Bajarin makes a strong point on using Siri with the AirPods:
There is, however, an important distinction to be made where I believe the Amazon Echo shows us a bit more of the voice-only interface and where I’d like to see Apple take Siri when it is embedded in devices without a screen, like the AirPods. You very quickly realize, the more you use Siri with the AirPods, how much the experience today assumes you have a screen in front of you. For example, if I use the AirPods to activate Siri and say, “What’s the latest news?” Siri will fetch the news then say, “Here is some news — take a look.” The experience assumes I want to use my screen (or it at least assumes I have a screen near me to look at) to read the news. Whereas, the Amazon Echo and Google Home just start reading the latest news headlines and tidbits. Similarly, when I activate Siri on the AirPods and say, “Play Christmas music”, the query processes and then plays. Where with the Echo, the same request yields Alexa to say, “OK, playing Christmas music from top 50 Christmas songs.” When you aren’t looking at a screen, the feedback is important. If I was to ask that same request while I was looking at my iPhone, you realize, as Siri processes the request, it says, “OK” on the screen but not in my ear. In voice-only interfaces, we need and want feedback that the request is happening or has been acknowledged.
Siri already adapts to the way it's activated – it talks more when invoked via "Hey Siri" as it assumes you're not looking at the screen, and it uses UI elements when triggered from the Home button.
Currently, activating Siri from AirPods yields the same feedback of the "Hey Siri" method. I wonder if future Siri will talk even more when it detects AirPods in your ear as it means only you will be able to hear its responses.