After a couple of minor teething issues with the QHY8 pro (faulty power cable and trouble installing the drivers) mine is now working well. Theo was very helpful in getting the cable resolved although I had to send the camera and cable back to him the day it arrived
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I agree with Mike - there is a big cost difference between the SX and the QHY8 - I guess that is in the quality control department.
I'm now happy with the choice I made.