It is easy to say "just go for it". In reality, it is quite risky.

Theoretically, it is possible to unseat a competitor like Google in search, or Facebook in social networking, but you really have to know what you are doing.

In your case, a better approach is to do some customer development first. Speak to potential users of your product. Find out if they are dissatisfied with your competitor's offering. What will it take to switch.

After that exercise, you should be in a better position to make an informed decision.