We have an E at Mike's Gym. It's nice... higher off the floor, connection between front and back is a little simpler and easier and doesn't have that stupid cam piece that tends to loosen up, monitor can connect to others wirelessly.
how it functions is really no different in any significant way. in fact, we had to send back the original monitor and have it replaced a couple weeks after we got it because it wasn't recharging. also, seems minor, but the way i used to move the Ds is by grabbing the back leg things, which would allow me to push/pull it but also twist it to lift one front wheel to get over smal obstacles... the new one is not as rigid in this manner and i have to just pick up the whole damn thing.
i would say save the extra few $ and even try to find a slightly used D.