We use MUS and really really like it. So far we've done Primer, Alpha, and currently somewhere in the middle of Beta. We'll probably end up skipping some of the lessons (or use them as quick review) in Beta since ds already knows how to skip count by 5 and 10, understands money, and can tell time. Ds is a very math-y kid. He sped through Primer at alarming speed. LOL! He understood place value right away. He is very a visual/kinesthetic learner. He has asbergers. I think he probably would do well with any math problem, but I really like the dvd's to help me tech the concept. I think a color workbook would have been a huge distraction. He loves the blocks. And he adores Steve Demme. He actually watches and rewatches the dvd's on his own. We're going to keep using it until it stops working. I will say that I made a mistake in not maling him memorize the math facts as we went along. We're still working on the last few subtraction facts but I let him move on since he was getting bored just reviewing facts. He should have them all down by the time we get to double digit subtraction in Beta.
I'm planning on using it with dd. She's 4 so we probably won't start for at least another year. She already has all the blocks memorized and hands them to her brother when he needs them. If it doesn't work for her we'll move on to something else. I kinda like the look of Singapore and may use thier Challenging Word Problems for ds along with MUS. He has a hard time with word problems, but can do them once I help him decipher what is actually being asked. All those words seem to throw him off. LOL!
I was more drawn to MUS because of the dvd's and support. I am not a math person. I took 3 years of Algebra and still don't really know what I was doing even though I aced the classes.