There are others as well Rheem and Ruud have one out and AO Smith has announced they are coming out with the Voltex heat pump water heater.
All of these units are pretty much the same having a 50 gallon tank and 2-4500 watt elements to offer higher recovery and ability to operate at lower temperatures where the heat pump would ice up.
The only unit offering a substantial difference is the
Stiebel Eltron Accelera 300 which has an 80 gallon tank and only a single 1700-watt element providing back up or, additional resistance heating. This unit requires only a 15 amp circuit for operation and provides a first hour delivery similar to the others. However this unit would not be well suited for use out of the southern tier states but if used in the right climate would be the most efficient operating one out of the bunch.