Has anyone here ever used math manipulatives?

Yes, they're called measuring cups, rulers, knives, drawing software, money, stop watches, grocery stores.

Oh, Mortensen! The math program. I think if you see the Mortensen manipulatives as no more important than the "manipulatives" I mentioned and are comfortable with your kids playing with the program for 5 minutes and then never touching it again, and you have some disposable cash, then you should get it ;-) If you think of Mortensen as a way to learn math you're going to be disappointed unless your kids think it's the bees knees and do it the "right" way. If, on the other hand, you know they will learn math from living life -- and you learn to recognize math in real life! :-) -- then Mortensen is just another thing to goof around with, as important in the great scheme of things as dice with more than 6 sides. (They're cool and nifty but no child's understanding of math depends on them.) So, of course, why spend the money! ;-)

I'd HIGHLY recommend the Miquon Math program with the Cuisenaire rods.

And I've recommended it many times over the years to homeschooling families. I think it's close to helping kids learn how numbers work but since it's on paper, it's still got that abstract quality to it that won't necessarily translate to understanding how it applies to things in real life.

What it boils down to is that it's still a program. It's designed to get kids to think about numbers in a particular way. If the kids are ready, if they can understand numbers that are divorced from real life, if it's something they enjoy it is designed to help them discover connections themselves, but the environment they make the discoveries in is still artificial.