they're eye opening, that's for sure. once i tried it i was hooked on the effectiveness.
but, instead of dropping the $40 on one, two wooden blocks about the size of a brick are better IMHO - you can move them around, flip them on different sides for different heights and... approaches. when you get one of the pre-cast plastic molds, it doesn't have much range. and $40? please.
i find the need to adjust from time to time - and you can slip the blocks away after use so it doesn't sit there and dominate your bathroom landscape.