This is for the internet connected ethernet bridge- uploads data to our servers, then you can view in the website, view in the app, share with others, share with weather underground, etc. It's free for up to 3 physical sensors (not just 3 weather data points, for example-a 5-in-1 sensor provides temp, humidity, wind speed, wind direction, rainfall- but is still just one physical sensor).
The USB bridge connects to your computer and provides data to your computer for free (less the cost of the bridge obviously) that you can record and view locally. Additionally, you may port this data out, or still have the option of uploading the data from 3 sensors for free to our servers, portal (acu-link.com),app, wunderground.com,etc.- same deal as ethernet bridge but through your PC's internet connection (PC must remain on for streaming).
The USB display works the same way as the USB bridge.
Hopefully this kind of clears it up for you- there are a few different options here to cover the bases. Let me know if you have any more questions.