Reservations are required for afternoon tea. You have to call or show up in person. They don't have an online reservation system. We made reservations one day ahead and it was fine. $35 per person includes tea, sandwiches (you can pick 4 from the 7 on the menu), scones and sweets.
The ambiance can be better since you are sitting in a casino bar but service was friendly and the food was good.
I've been to the Veranda and Mandarin Oriental for afternoon tea as well and would rate this place #2 out of the 3 but I feel this place tops the others for value. My #1 would be Mandarin Oriental but it's more formal (not required to dress up but it feels that way), cost more (it's about $40 per person) and they give you less food. However, the food you get looks way better (taste is about the same) and you get a nice view of the strip and you can make a reservation online.