[Nateman]

...the electronvolt is also a unit of mass

No. E=mc^2

[zeestephen]

Re: the electron volt is also a unit of mass

Re: No. E=mc2

Actually, physicists use the electron volt to express extremely tiny weights because they would have to use long strings of zeroes (0.0000000 etc.) if expressed in grams.

Electron volts are conveniently written and easily understood.

And, as you point out, energy and mass are interchangeable.