terminal length (rate of growth x life span of a hair) is highly variable across individuals. while there may be averages out there, none of them give a definite answer to what your terminal length is. if your hair is not getting any longer, i would try other methods to see if it's a retention problem. i would give each method a long enough time to really notice a difference (at least 3 months). if after a year or two i had seen no gain in length, i might think that this is it for me.