Hello 
Yes it is good to do mechanical diploma after 10
Because one can directly go for a good job after diploma. Taking Mechanical can help you get into core companies. A diploma holder is considered as a junior engineer. You can get government jobs easily. The best part is if you want bachelor after diploma you can directly get into btech 2 year of the course.
So with diploma you have a secured future better jobs and multiple career options.
Hope this helps
Good luck