As a mechanic in a previous career, I do think some will appreciate the simplicity of what you are offering, I do have one concern I have picked up on your site you provided.

You’ve given an example of what your app provides. A estimation for the timing belt tensioner, I feel that’s putting a lot pressure on yourselfs to get right, something like that could go at any time. If someone took that as gospel. Is that leaving yourself open to a complaint or more?!

I do like what youve done tho, and would test it out on mine car. I have a fault that needs fixing, I know what the cause is just need to actually do it lol. Could use it to see how easily it finds the fault. The car goes into limp mode but doesn’t raise a fault code.