Note: Edited since first posting as the ND filter is not missing (doh!)
Based on positive reviews I ordered the visual version through AliExpress. It cost about $230 including shipping and GST.
https://www.aliexpress.com/i/4001204285379.html
On opening the package I discovered:
- the 'included' polarising filter is missing
- the main body enclosing the prism is loose at every joint
I was able to solve the second issue by tightening the various tiny Allen bolts so it now feels secure.
AliExpress has offered a partial refund for the missing filter so I guess if it performs ok then I'll probably accept it.