"No, he probably will not. The element is rated for 208V. He's going to
pushing a fifteen percent overvoltage through it, and it's probably
burn out very soon. "
I seriously doubt that a 15% overvoltage in a heating element that is
surrounded by water is going to burn it out. Just because the instant
water heater is labeled for 208V, doesn't mean that's the max rating of
the individual components, like the heating element. As an example,
some SPA/Hot Tubs are sold as either 120V or 240V. They are identical
except the power packs are slightly different. Both units have the
exact same heating element. If you look at the label on the 120V SPA,
that's what it will say, even though the heating element can take 240V.
You can switch it to 240V by simply changing the power pack, leaving
the heater element as is. In that case the heater then puts out 6KW,
instead of 1.5KW when wired for 120V.
BTW, I'm not saying I'd used this Ebay water heater myself, only that
IMO, it's likely it would in fact work.