The problem I see with the 841 is timing. If it had come out a year ago, or it had done 18+ TH, it would be awesome. But it's taken 1.5 years since the S9 for canaan to come out with something that just barely beats it.
Presumably Bitmain has also been working on something quite a bit better than the S9. And we all know how they like to crush competitors.
True, everyone has to make their own decisions about where to spend their money based on their own logic and experiences. I for one am completely fed up with the crappy hardware Bitmain puts out. Fully 38.5% of my antminer S9s are either dead or have serious failure issues and they have all run in a professional data center from day one. My Avalon equipment are just steady and boring...they just produce above their specs everyday.
EDIT: I didn't include my S7s above because they are older. They are at a 50% fail rate.
EDIT2: No one likes to factor in equipment failure in their break-even calculations. What do you think a 38% failure rate does to those calculations?