From what I've seen happen at the track, they are a 50/50 bet.
In a lowside where they just slide along a smooth surface, they seem to work well. In a lowside where they slide and catch a kerb or similar, they can cause flips.
Depending on a million variables including the brand/type of slider and where they attach, they may or may not damage the frame.
And you have to bear in mind that sliders ain't sliders. Many brands claim to be made of "a low friction material" and reckon they'll let the bike slide "smoothly." LSL, among others, by comparison use high friction material to slow the slide as quickly as possible (I can see the logic in this) and an asymmetrical design that supposedly helps stop the bike spinning as it slides.
I have done some thinking and chosen to run sliders ... I also run full GB Racing engine case protection.
O.B