Installation is very simple, just install and activate the modules in the normal way.
The Yahoo YUI module provides base services for several modules using the YUI toolkit. This module has one configuration setting, which is the location from which to retrieve the YUI javascript files. By default it retrieves them from Yahoo's website, but this gives you a risk of slow response if Yahoo's server is busy. You can put the javascript files on your server and if you do make sure to change the URL in the Yahoo YUI settings.
The YUI Rich Text Editor settings lets you control to which text areas the YUI editor is applied. By default it applies itself to all textarea's but it can be controlled.
This editor is subject to the issues raised on: Conflict between WYSIWYG and Line break converter
The editor works fairly well.
It has some UI clunkiness in that there are not keyboard accelerators for the toolbar buttons, and clicking on toolbar buttons causes a loss of keyboard focus. Clicking on toolbar buttons requires you then click in the text area again so that text is entered in the textarea.
The editor uses <br> tags to mark paragraphs, rather than using <p> tags. Bleah. This is so incorrect it's not funny.