Hi Hadyn,
I've just taken delivery of a 2019 ZS73, matching uniguider and 73A adjustable flattener. I've not really had a chance to try in anger yet due to this week's horrific weather. During a brief break in the clouds I did manage as far as taking a photo of the moon through an old Skywatcher eyepiece using a Samsung Galaxy S8. Visually it is lovely and sharp the Moon terminator standing out nicely. Build wise this a quality bit of kit, everything feels well made, the focuser feels silky smooth with no backlash.
There's little in the way of manuals or decent descriptions on WO website but I think I've figured out the adjustable field flattener should be set and locked to 11.4mm then space from the flattener M48 thread to sensor should be 66.2mm. I have a Hypercam 183C Pro Tec and had to order an extension piece to achieve the correct spacing. It's a never ending drain on the wallet.
Roy