One is from Rheem (sold at home depot) and the other is from GE (sold at Lowe's).
In fact they may be made by the same company. (Rheem makes some of the GE branded water heaters they sell at Home Depot, just look at the installation manual.)
These systems work a lot like a window air conditioner except instead of the heat going outside it goes into a 50 gallon water tank. The improved efficiency makes them equivalent to a natural gas water heater in usage costs.
The prices for hybrid water heaters may look shocking at first -- from $1,440 to $2,500 -- but they're eligible for the 30 percent federal tax credit plus the state 'cash for appliances' rebate as well as other state and local incentives. Unfortunately the State credits in Michigan just ran our for 2010.
That may have brought down demand. What I know for sure is that both the Rheem and the GE units are on sale this month for 10% off.
These units really shine when you look at operating costs over their lifetimes. Hopefully they won't take much service and they will last 10 years or more. In which case the overall cost will be much less than a conventional electric water heater and probably even less that a natural gas water heater. (Of course that will depend somewhat on what fuel prices do over those same years.)
There is another option with heat pumps for water heating, that is the add-on systems. Both Geyser and Airtap have systems that can retrofit an existing electric water heater. The Airtap costs about $700 and the Geyser costs about $1,400. But if you are going to consider the GE and Rheem you should consider these too!
And don't forget about energy tax credits!