that you find on fleabay?
Seems counterproductive to build your own unless it does something these bluetooth devices don't do….I'd love to see a library for accessing those bluetooth devices…
For the record :
Not all computers have bluetooth. While I don't know which precise interface you are referring to, it's probable that a quality bluetooth-OBD adapter is going to be either expensive or not very flexible. The goal of freediag is not just to get DTCs and clear them.
One example of what you could do with freediag is send manufacturer-specific requests that are not necessarily defined in J1979, that would otherwise be difficult or impossible to send with a "random" bluetooth device.
I won't pretend freediag is the ultimate solution of vehicle diagnostics, but it's a tool that certainly has its place.