I only had a chance to look through it briefly, going through the main menu (the links), probably for about 10 minutes or so, and so far it looks pretty useful for a student taking an Algebra course. I looked at the links provided, and it's pretty useful for both student and teachers who want to review the algebraic concepts.
The content is pretty simple to use. Under the main menu, there are links that takes you to the different concepts, which provides an brief explanation about what it is, and then continues on to show examples of how it is used in the math. It takes you from angles and circles all the way to vectors, and although it is not as thorough and detailed like it would be in a textbook, it does provide to be a good reference. They even have math games and riddles for the student to ponder and try out as well.
It's effective as a reference, and maybe a brief study on the concepts before taking it head on in a math course or text. A student can prepare him/herself using this site.
The layout of the site isn't as intuitive as other sights, so it might be a little harder on the eyes to navigate around. But once you've learn to navigate around, it makes it a lot easier for you to bookmark and figure out where to go.