You need to be aware that mining depends a great deal on "luck" and "difficulty". I mine with a full unit and one standard and track my results on a daily/weekly basis. My "best ever" week was March 30 - April 5 when the two units "mined" 0.00020829 BTC. The average with 2 units has been 0.00017008 BTC per week. At the current USD price of BTC that's about $5.00.

Obviously your "profitability" will depend on your cost of electricity (200 watts per unit) and how you choose to account it. I suggest that you treat these miners as variable rate foreign currency bonds with a *very long* duration. The simplistic "ROI" you see everywhere is really only relevant at the commercial level of mining.

Good Luck!