GavSt: that type is OK though less effective than a petal-hood at the wide end. Also, when folded back for the wide end it doesn't take much to make it spring into standard mode and cause vignetting (dark corners) with perhaps 35mm or wider focal length.
They are longer than most rubber hoods, so well worth having for longer lenses.
You should think about getting one to fit the largest diameter lens you are likely to own (82mm or 77mm) and use with step up rings on your other lenses. This can help avoid any vignetting on your wide angle lenses, as well as saving you having to get several hoods (though the step up rings aren't much cheaper).