The Sonicare 4100 and 5100 are quite similar, but a few features separate them. The 4100 has one cleaning mode. Although it produces the desired results and some users like its simplicity, others may prefer a model that offers them various cleaning modes. The 5100 offers that variety with three different cleaning modes. The 4100 lacks in that aspect. Apart from that, this model does not come with a travel case, while the 5100 comes with one. Also, the 4100 comes with the C2 Plaque Control brush head, while the 5100 comes with the Gum Care brush head.