Here is a live link to the 80 gallon model:
http://www.stiebel-eltron-usa.com/accelera.html
Looks like a well built unit. The thing I like most about this unit is that the incoming water is plumbed in at the bottom. When hot water is drawn from the top, the cold water naturally stratifies and stays at the bottom. Also, the unit doesn't have multiple modes to set, it just works like it was designed to all the time. Less gadgets inside means less chance for malfunctions.
As far as payback goes, hpwh are not much cheaper to run than natural gas. Due to the fracking craze, natural gas is cheap for the time being. This may or may not change anytime soon. Also depends on your grid power rates and local gas utility.