Well, after using Taconic shampoo bars for the last couple of months, I've made curious discovery. My sister who's been cutting my hair for the last 12 years noticed that I had a lot of new, tiny little hairs growing around my crown (I'm not balding, but I have noticed a lot of thinning the last couple of years). Coincidence? Possibly. However, the only thing that's changed in the last 3 months is what I've been using to wash my hair. I think it stands to reason that eliminating artificial ingredients and preservatives stimulates hair growth.
Also, if you're wondering how long this will last, one bar, even used generously, will easily last you two months. If you just give it a pass or two, you'll probably get 2 1/2 - 3 months out of it. I also weighed a new bar on my kitchen scale and it came in at 5 3/8 ounces - so their 5.5 oz claim is spot on.