I'm using these rods to help my daughter (6 years old) with number sense right now. I've found them to be pretty effective at helping her build the concepts around manipulating numbers for arithmetic. The only pitfall we've run into was in connecting the manipulation of the rods with the manipulation of the more abstract numbers.

They've really helped in the area of modeling the problems. Depending on where you put the unknown, there are several ways to ask the same arithmetic question, eg:

    _ + 2 = 5
    3 + 2 = _
    3 + _ = 5

Using the rods to model the knowns and unknowns has been really helpful for her to connect the abstract ideas of the equations with the reality of what the numbers mean, and how the manipulations work on each side of the equality.

Overall I think they're a pretty powerful tool, but they require some creativity to really get the most value from them, and they definitely require the use of other learning aids in conjunction like number lines, 99-charts, and base-ten blocks. We also use money, marbles, and other things to try to avoid getting too dependent on a particular manipulative.

Actually the biggest breakthrough we had was making up a card game to learn complements of ten. If you've played "set" you know the basic idea - we lay down 12 cards numbered 0-10, and we compete to see who can make pairs or triples that sum to ten the fastest. She loves it, and she's gotten to where I really have to work to keep up.