I found that the search result to be somewhat inaccurate using relevance setting from the plugin.
Is there anyway for me to use the wordpress logic as default search algorithm?
The feature that I really need from the plugin is only Live Search and also the caching function.
You can experiment with the keyword logic options under the General Options -> Logics & Behavior panel. The default options are very similar, almost the same as the default WordPress search logic, except the relevance.
If you prefer, you can turn the relevance off entirely under the Relevance Options panel as well.