I have synthetic vision installed in an EC120 as part of the Flymap system. I have used it in good VMC both "down south" - where it is not shown to its best effect because we don't have much high terrain to worry about - and when flying through the Scottish hills & glens (valley) - where it is quite impressive; particularly when flying along a glen.
It might indeed be an additional help during inadvertant IMC but I have no intention of finding out.