921 more or less efficient than the s9j? Essentially this unit is best compared when looking at T2 or the turbo at 24th/s. Essentially cheap hash to watt or dollar/BTC.
Mid range unit and typical Canaan price to market to sell. You know it's a solid unit and probably the x amount you buy will work a long time with moderate maintenance. If your starting a farm right now it's worthy to consider.
Edited for typo and to reminder everyone it's 1800w again.