For anyone wondering how reliable Bitmain hardware is... I've been uber impressed with the PSUs in general, but today one of my PSUs' fans packed up. It literally just stopped working. I didn't notice until I went into the room and saw the lights off on the machine and the PSU was hot to the touch. I took it apart, tested the output to the fan and got 12v, then tested the fan on another PSU and confirmed it was faulty. Luckly my local electronics supplier had an identical 60mm fan - it's probably marginally less powerful, but it's working fine - the PSU doesn't get that hot on the inside. R70 repair.
So there you go - stuff happens when you run anything 24x7. That was way sooner than I had hoped to be honest.
I am a bit bugged that it doesn't appear to have it's own auto shutdown - it's pretty simple... unless the fact that the machine was off is an indication that it does indeed have a temperature sensor and auto shutdown... not sure. I'm going to use my Pi Zero and DH-22 sensors to monitor and shut it down in future.