I heard about XtraMath.org from God-knows-who or where and wanted to try it. I had been avoiding math for a long time due to having baby after baby and losing brain cells left and right. So I was at a point where I was checking out every math program that came my way, especially free ones (by the way, we have settled on CTC Math, and you can find that post here).
Immediately my kids hated this. It's timed drills and my kids feel so pressured and stressed with timed stuff (well, the oldest two, anyway). Then the public school kid comes over and is like, "Hey, we use that at my school."
At first I was like, we are going to forge ahead with this because memorizing times tables and such is VERY IMPORTANT.
Then when they were literally in tears every time I turned it on, I said, SCREW THIS. So this is what they do in public school? M'kay, that seals it for me. I don't WANT TO BE LIKE PUBLIC SCHOOL. There is a reason I am homeschooling and it's to be DIFFERENT and ... sorry, school friends, but I have to be honest and say ... BETTER. And better to me means more relaxed but still learning great, important stuff.
Bottom line: if your kid likes timed drills and thrives on that kind of stress, go for it!