OK, returned the III on Tuesday, shop didn't have a II in stock so they refunded the item. According to the WO website, the PflatII is their best option for the ED80.
Perhaps I'll stay with prime focus for a bit longer, but I also think the Mogg flattener seems good value for money so I may try it out.
The Borg flattener looks like a beauty but as mentioned it's a bit pricey compared to the value of the ED80. I'll dream about a larger refractor with a matching flattener.
Cheers,
Rob