I had been thinking about getting some Cuisenaire Rods and then saw that they were highly recommended by several people on the teaching math thread. At least on amazon there are so many to choose from wood, plastic, plastic locking. I'm looking for recommendations what type? I like wood things/toys (and, an added advantage, they make a lovely sound for small boys) but can see the advantage of the locking ones. What do the lovely HE-edders of MN think?