Sharon Cohen, the brand manager at Orbeez, checks in on the last post:
The disparity (150/100) is based on the fact that growth depends on ionic content of the water–the purer the water the larger they grow. The very same Orbeez wll grow to a different size depending on the water purity. The number we chose ended up being a marketing decision (100 is a powerful figure) but we should have been consistent. It's impossible to choose one accurate number.
BTW: Sharon Cohen sent along Orbeez' internal measurements of expansion given different water sources.