If you haven't got a tumble drier/no space for one, it's great - much easier than without. If you're thinking of getting one to supplement a tumble drier... forget it! I've found the best way is to use alternate arms (so you're only using 3 of the 6 arms to dry 9 hangers' worth not 18) & use it more for finishing things off (after first putting on airer in bathroom with dehumidifier).
I have one. It does work, but not when you have it completely full (18 items) unless they are things like cotton shirts, lighter items etc. Jeans, fleeces etc? forget it! I find my 28 year old tumble drier is quicker for things that can be tumbled and even hanging wet clothes on an airer with limited central heating on is quicker. Also, the DriBuddy takes up quite a large area of the room it's in.