Crikey that was quick Chris.
The power distribution board that I got from a seller on Aliexpress took 48 days to arrive (see picture above), but had been sitting somewhere in Australia since the 25th October (probably customs). Having said that, all my orders that I paid for EMS shipping are still only taking about 1.5 weeks to arrive from the date of payment.
I don't think the error on the sonar will cause any issues, because as I noted before, the error is consistently around 25%, which means the shorter the distance, the smaller the error.
You have to select the LV-EZ0 sonar in Mission Planner to get the HC-SR04 sonar with the additional board from Thanksbuyer to work. The documentation for Arducopter states that selecting the appropriate sonar is so the correct algorithm is used to get the correct scaling for the sonar you are using. When I selected other sonars, I got similar errors, but the sonar distances where much further out when compared to when LV-EZ0 was selected.
Now to my mind being a programmer for nearly 30 years suggests to me that that statement suggests that the possible problem area may be the Arducopter firmware, and that perhaps it may be able to be corrected by customising the firmware. I may have a look at this at some point in the future.
The fact that different scaling is used for different sonars would suggest to me that it is quite fixable to someone who can interpret where this scaling is applied in the firmware.