W is for wireless as has been stated. Although I run 2 in my 100 you likely could get away with 1. With the new ES controller they have several new pre programmed modes. With 2 you can sync them together wirelessly so that when you change modes on one you change both. They also operate in a way that when one is going full blast the other isn't. You can create waves and such when you have two in operation. I have four running at the store and when I put one in feed mode they all go into feed mode automatically. Vortechs are a great investment for sure. I fully endorse the product.