My son has used IXL at school, and has an unfavourable opinion of it. The subjects progress too slowly, which can be problematic if you have to meet a given benchmark of completion to "prove" mastery. I much prefer pen and paper options, like Sinagpore Math, which have end of chapter tests that allow you to test out of levels quickly.
We've also been required to sign up for Redbird's new version of EPGY at my son's school. I've been unimpressed with the GUI, to say the least, and have spent several hours troubleshooting a technical issue on their end.
