The original, been on the market already for a few years, is > https://www.upfallshower.com/en/

But is way too expensive. +€4000,-

Hamwell gave up their e-shower and only has now a camper version https://hamwells.com/en/loopz

https://flow-loop.com/the-loop-shower/ promises to be far more affordable (and is backed by IKEA) , Australia too is waking up http://www.recyclingshower.com.au/ More will follow, once it goes mainstream.

So Rainstick's price tag will come down. But I'll admit, the market for this solution is huge, as it's one of the critical missing links for efficient home energy.