WikiDash is a fast, optimised dashboard/interface for Wikipedia packaged as a Google Chrome extension. It is intended for power editors.
There are several reasons; some personal and others pragmatic.
The main reason is that the Wikipedia UI is slow and tired. It's designed for all users; from casual editors to readers. This means that it is poorly optimised for power editing.
Plus it has "funny" behaviours like "I'm going to suddenly sprout messages at the top of the page pushing all the content down" or "what do you mean you wanted 'my contributions'? So what if I moved the logout link under your click..".
Part of the problem is that a lot of the UI is loaded and modified using Gadgets; power users utilise these to make the interface more accessible, but the downside is it becomes slow and buggy.
Wikipedia features a wonderfully comprehensive API - it will let you do all the same things as the web interface, but often a lot faster.
WikiDash is packaged as a Google Chrome extension; this means it runs locally in your browser (i.e. not via a 3rd party server) and all edits are authenticated via your usual Wikipedia login.
Is it secure?
Yes. The password is sent to direct to the Wikipedia API via HTTPS - it is not stored locally.
If you logged in via the web interface then this step isn't even required (as that login persists). So if you are particularly security concious please do that.