Hi Split,
They do seem to work on the STOXX, but will be breached often in strong trends or only provide a minute or so respite. Also they act on STOXX (and I can only speak for that as it's all I have used them for) within a 4/5 point band, so you can't be exact with them. Then again you can't with any other sort of S/R. My attitude is it's worth knowing where they are, lots of people use them so they are likely to be "sticky". Same things applies to yesterdays, H,L,C values. It's all additional info that can make a difference between profit and loss and you need all the edge you can get.