I've done some searching at https://www.waterrating.gov.au to confirm my statement in the earlier post.
All new products — where the product has been manufactured or imported into Australia on or after 1 July 2006 — must now be registered and labelled under the WELS (Water Efficiency Labelling Scheme) before they can be sold. Products covered under this scheme are skwers, taps, flow controllers, toilet & urinal equipment, washing machines and dishwashers.
If the rain showers you're looking at have a WELS label you'd have to think they work?!
All this has reminded me that I'd like one too…