MTG, well, I don't particularly like it for mane/tail use. I think it's greasy and very stinky. Going on it is okay, but the next day the horse (and your hands) will smell like sulpher. So I got sick of using it on their manes/tails. Also, one of my horses is a gray, and like anything greasy, it attracts dirt really bad.
However, just when I was about to toss the tiny bit left in the bottle my gelding got scratches on his pasterns. So I started using it for about a week and it did seem to help. It wasn't an overnight miracle or anything, but there was steady progress in the right direction. But then I used it up so I am going to try something different for his scratches problem.
I reasearched MTG a bit before I bought it, and basically it is a spin-off of a treatment people who keep draft horses use to keep them from getting scratches and skin problems in their feathers. I think they call it sulphering or something. The main ingredients are sulpher and mineral oil. So it is something I think someone could make pretty easy if they could find the sulpher, but apparently draft horse people have a similar recipe.
I think, if I wanted to go for something oily just for mane/tail detangling I would just use plain old baby oil or mineral oil. Cheap, easy to get, shiny, detangler that costs 1/16 of the price of MTG.
So as a detangler MTG doesn't impress me. For a mild case of scratches, it showed progress. For growing hair, I highly doubt it! If it did, then they would be marketing it to people like Rogaine. There is a lot of money to be made if you have a product that actually grew hair. If it grows hair I believe it is only because it is treating an underlying skin condition.