WordPress.org

Why should I use this plugin?

Use this plugin if you want to get rid of WordPress' "Category base" completely. The normal behaviour of WordPress is to add '/category' to your category permalinks if you leave "Category base" blank in the Permalink settings. So your category links look like myblog.com/category/my-category/. With this plugin your category links will look like myblog.com/my-category/ (or myblog.com/my-category/sub-category/ in case of sub categories).

Will it break any other plugins?

As far as I can tell, no. I have been using this on several blogs for a while and it doesn't break anything.

Won't this conflict with pages?

Simply don't have a page and category with the same slug. Even if they do have the same slug it won't break anything, just the category will get priority (Say if a category and page are both 'xyz' then myblog.com/xyz/ will give you the category). This can have an useful side-effect. Suppose you have a category 'news', you can add a page 'news' which will show up in the page navigation but will show the 'news' category.

Can you add a feature X?

Depends, if its useful enough and I have time for it.