My Take
I like how IXL can be used in various ways. It can be assigned for homework, used as a math station in class, used to review concepts or to extend them. Students like earning medals and are more motivated to complete problems on IXL than ones that the teacher assigns. I also like how I can choose to have the grade levels show up as letters instead (Level A, B, C, etc) so that students don't know what grade level skill they're doing. This is particulary helpful for students who need to work on skills far below their actual grade level.
How I Use It
I assign IXL for homework, which poses problems for students who do not have Internet access at home. But it works great for students who have Internet access at home. I also use it in class when differentiating math instruction. Sometimes I'll have students who have already caught on to a lesson practice problems independently on IXL. Then that allows me time to review with students who need more instruction.