According to Tim Cook, CEO of Apple, AirPods have been a great success so far. They have been a big hit to the point Apple cannot keep up with the orders, and they(Apple), are running at full capacity to make the AirPods as fast as they can to meet increased demand.
That could be true by all indications on the ground as Apple is running on a six-week delay in shipping, and that was just one week after the launch. That delay has continued to date, and even in-house product pickups for AirPods have been pushed to mid- February when they will be available again.
But that does not necessarily mean they have been a success. The ability of how many units Apple is manufacturing the AirPod is what counts and at what rate. If the rate is slow, delays will be encountered even for a demand of a few units.
Apart from Apple, no independent source has any figures that show AirPod is a great success and efforts to request for exact numbers from Apple have been futile. Apple could also not provide information whether, in their next earnings release, Airpod figures would feature.
This is usually intentional, though, and it can be used to mask failures without necessarily going public. Particularly when new technology, which is a usually a first is concerned. That is how Apple has been working lately. If the figures are made public, it is because Apple has done well. If they do not avail the numbers, your guess is as good as mine over what might have transpired.