What do you ladies think of waist trainers? Do they really work?

It looks like the new trendy crase amongst ladies these days in the waist trainer...recently made popular by Mrs West. Ladies are now wearing corsets for hours at a time, some even to bed, to help compress their core, which is supposed to eventually shrink their waist and give them that hourglass figure (like Kim), but is it safe to wear it all the time and does it really work?