I was really interested in MathUSee also so interested to see what others posted below.
I bought Math In Focus for this year (ony half a year, a grade level lower since ds is behind, and I'm not loving it). It is a Singapore method that is supposed to be good for visual learners and mastery. The problem is I bought the second half of a grade level lower, and it wasnt the best choice. My son really needs to improve his number sense, re-learn all his math facts and doesn't know his times at all, so the second half of last year has none of that - it's money, measurement, fractions, charts and graphs -- essentially all the things that I think aren't so imperative if a school is using the program and doesn't finish by June. I think I'd have been better off getting the first half of a grade level lower.
I am not using the teacher's manual at all so far. We are harldy using the textbook either. We are just using the work book and not even consistently since I think our time is better spend on math facts (even addition and subtraction!) Plus I have lots of manipulatives which we use a lot. I got MathInFocus cheaper on ebay, but not looking forward to buying 1st half of 4th grade in another two months and paying like $150.
SO anyway, I bought a pdf download of Mammoth Math multiplication blue for $5 and love it. I might print it off again and have him do it twice or more! I'm thinking of making his sister in PS do it too.
Frankly, I am bad at math and recall having terrible math phobia in school. I've been researching a ton and think my son is a little beyond math phobic and may even have a touch of dyscalculia. I think I may have it too, but this esperience is making me realize whomever taught me were really good teachers at the elem. level. I seem to have been taught Touch Math and a lot of other ways to figure out problems and I think mastery of facts was the emphasis way back then. So, I"m sort of in the camp where I'm willing to HS as long as it takes and I'm not expecting ds to become a mathemetician, and I got by fine in life and can do some basic mental math now and do fine with my basic math skills and can do my personal banking, taxes, problem solving and logic. Frankly, I bet if I took an algebra class or something now, I'd do pretty good. I always was an ace at geometry.
Well, long way to say I'm leaning toward Mammoth Math because everything I read makes it sound so straight forward - no teachers manual or textbooks, just one workbook. I heard it reviewed as like a lighter version of Saxon. I like the look of some other programs like Teaching Textbooks or JumpMath looks very intriguing - but I think we'd be lazy with putting in the dvds. I know I have the where-with-all to seek out support if there is something in her books I can't teachor get across to ds... seriously, I guess I'm lazy in this area and am swayed by MM's low price!