Bought this to augment the terrible built-in system on my Toyota, and it mostly works. As others have said, this is little more than a microphone attached to your phone that works with the phone's Alexa app, however it makes it easier to use Alexa features.
What you it lets you do: Makes it easy to control streaming music ("Alexa, play songs by ..."). Once playing, hitting up and down on the car's audio controls on the steering wheel lets you skip songs. Basic Alexa queries like "drop in", "weather", etc all work here. Note that others cannot drop in on you, however. The sound cancelling does a great job of blocking wind noise, much much better than the phone itself. You can have it read recent text messages, but *only* if you use the default messaging app that comes with your phone. If you rely on other apps, like Mood or QKSMS, maybe even Signal...it will just say there are no recent messages. It is supposed to allow you to make phone calls and send text messages using voice, although in my case the app keeps asking for permissions it has already been granted, and I've never quite figured it out. If your contacts also use Alexa then messaging is easier and more seamless. YMMV.
What you can't do: Navigation. Sure, you can say "Navigate to ...", but all it does is launch Google maps and let that do the work. From there, you need to look at the phone and the voice control is spotty. You can sometimes say "cancel navigation", and sometimes you need to manually intervene. You cannot do the full extent of features you can with Google's Assistant (for example, send a message using Telegram). It also will not interrupt your regular radio, so your car has to be on bluetooth (or extenal input) in order to use this, which makes navigation more painful. If you've every used the old Blackberry Assistant, or even Windows Phone to do this kind of thing (they both used a special phone # 555 555 9876 to "call" your car over its phone connection) then you will be shocked that years later, this doesn't work as well (in fairness, Google Assistant doesn't do that either).
Installation: The included clip does a great job attaching to my vertical vents, however the usb cable sticks out the right side. This means if you mount it to a vent to the right of your steering wheel, the cable may partially block a volume knob or button on your dash. I wish the port would have been underneath instead with a 90 degree elbow.
Summary: The Alexa phone app supports hands-free, and on Android, Google's Assistant does as well, so the question is whether you actually need this. Feature-wise, my experience after months of use is that getting Alexa's phone app (or Google's) to hear me in-car is frustrating. Google's in particular often seems to be unable to make sense of just about anything much of the time. With this, I never have a problem with Alexa hearing what I need to say. As I listen to a lot of streaming audio, I find this very helpful. If Google Asistant or the Alexa app already work on your phone hands-free, and work well in your car, then there is no need for this. If however, you find yourself yelling at your phone constantly then this is a good device that is worth the price when on sale. Overall, needs much better car-specific support to really make it shine though.