Vanes are not as pliable, will tend to deflect the arrow upon launch more readily than would a feather if there is any interference. Hence the suggestion of using vanes from an elevated rest, where interference may be more easily mitigated. I've not shot vanes from my bows, only have 1 with a NAP flipper on it, but have been tempted because they are so much more forgiving than natural feathers in the wet weather. But, as most others, that benefit is of limited value as most folks don't bow hunt while it's raining. And because feathers can still be effective even if a little wet, and can be kept covered realitively easily.