According to Focus Taiwan, the One E8 is “geared primarily toward price-sensitive markets”, but HTC could also use it "to maintain sales in the last half of the year in markets where the life cycle of premium phones appears to be shrinking.” Thus, the Taiwanese company might plan to release the E8 in more countries than initially planned.
The One E8 is a cheaper version of the One M8, costing slightly under $500 in China and Taiwan. Most of its features are identical to those of the M8 flagship, though there’s no 4MP UltraPixel camera on the back - this being replaced by a regular 13MP camera. More importantly, the E8 is made out of plastic, so it doesn’t have the metal construction of the M8. And that’s why it’s cheaper.
source: Focus Taiwan