Not quite. The WF only gives a -2 penalty to hit to those rounds in which you elect to get the extra attack. If you don't want the extra attack (i.e. if you can't make a full attack that round anyhow) then you just WF without the -2 penalty to hit.
As for how long it lasts, it is slightly less than a regular rage, simply because it does not grant a bonus to CON, like regular rage does, and CON bonus + 3 is how you measure the duration of either.