I have an very early model of the Sig 100w box and love it! The ONLY thing I don't like is the 510 connector, there are rare times it will read my RDA resistance as being much higher than it really is, and will adjust my voltage accordingly! Seems to happen only when I try to get the RDA to sit flush, so now I just leave a small gap underneath.
For this reason I would suggest spending the extra $10 or so and get the "Plus" version instead, as it has a spring loaded 510 pin.
And another thing that could be a con, no USB charging port. That never bothered me since I would rather use my LUC charger for batteries anyway.