I have downstreamed c austic as well but I don't like to ..I would rather use a pump up sprayer
For hoods maybe so, but for concrete you can't beat DS'ing for speed and even application. We DS hydroxide on concrete, but do use a pump up for pre-spotting heavy deposits. For that we use a REAL hot mix.
I have noticed that O-rings do go out quicker when DSing as well, but hoses get a good rinse so I haven't noticed any difference in logevity.