Shazam,
why do you prefer 841 over S9?
Reliability. The 841's are also a little more versatile, as far as, adjusting the frequency. You can get a bit more performance/efficiency. They are backed by a 2yr warranty, and if need be, replacing any parts is super easy. Plus Canaan supports Bitcoin and our Community. Great company. They've offered me a tour of their facility, and if I had the money to fly there, I would!!! Ha!!!
Yep, I now have all S9s and 841s. My 841s all run at 13.5+ but draw less watts than any of my S9s. The 841s are proving to be the most reliable machines in my farm just like the older Avalons were before I upgraded anything. I would love to have all 841s if I could