Well, it is VERY hard to say how profitable a miner can be, especially one with so many algorithms. For example right now DGB is crazy profitable ($52 per GH/day and going up, even with the +40% Dash price increase that "only" gives $36 per GH/day). Thus ROI can be reached in a month or two depending on what you paid .. which is way better than what I used for calculation (about 4-6 months). Obviously nobody knew DGB would increase this much and mining it would make sense. If you would have known you could have bought DGB at less than a cent and now have 20 times the amount of value, but that is stupid, no one knows. With mining you can switch to whatever makes most sense at the time, you only get screwed if the price drops before you can ever convert it.