Our experience with Math Mammoth: While I think Math Mammoth teaches math well, we did not like it. I think the amount of work on one page intimidated my daughter (1st grade). We dropped it when my computer crashed and I could no longer print her worksheets at home. I looked into having it printed at Staples, and the cost of one chapter would be $25, so that was not exactly a less expensive option.
We spent the rest of 1st grade with a variety of math resources. This year we will begin Math U See. I just received our material today and am looking forward to it.