Review in a nutshell: It appears that this is an upgrade of the Amazon Echo. I believe they have divided Amazon Echo to make it into 2 less costlier parts which are Amazon Tap and amazon dot. You can buy the one you want according to your requirements and the listed functionality.
1. The biggest difference is that the Tap is portable with a 9 hour battery life vs the Echo that is stationary.
2. The AmazonTap comes with cradle to recharge vs the Echo must be plugged into an electrical socket.
3. The AmazonTap has a microphone you press to communicate with the device. The Echo has a remote or voice command for communication.
4. The Tap has a 3.5 audio input plug vs the Echo does not have an audio plug.
5. The Tap is about half the size of the Echo.
6. Alexa only listens when you “tap”, is a portable speaker with its own battery, built-in speaker can play music from wi-fi/bluetooth/audio-in, no audio-out jack.
To make it a bit clearer. It has built-in high quality speakers but it doesn’t give you the freedom to talk to it from anywhere. You need to press a button before giving your voice commands. This can save you a bit of money versus the Echo if you don’t mind pressing a button to activate. The tap, when out of Wi-Fi range, can leverage your mobile phone to enable the Alexa Voice Service
Amazon Tap is an Alexa-enabled portable Bluetooth and Wi-Fi speaker that offers rich, full-range sound. Just tap the microphone button and ask for music, hear the news, search for information, order a pizza, and more with the Alexa Voice Service. Amazon Tap has dual stereo speakers with Dolby processing that provide crisp vocals, extended bass response, and immersive, 360° omni-directional audio. Amazon Tap is available for pre-order.