I have recently started to use the Retromixer.
It doesn't work extremely well but it's better than nothing. Whenever the water pressure is more than minimal, water tends to flow out along the top in addition to the bottom. And where it does flow along the intended bottom, the mixing isn't very good; I might get hot and cold water in rapid alteration in time and space. But it's progress nevertheless and I recommend it.
It's rather small and easy to install, so in principle you could carry one around for usage in public places, but it's marketed for use at your own home.
(I am not affiliated with the company making the Retromixer, nor do I personally know anybody involved.)