I would love to say the MTG works great, and I've only used it twice, but it DID NOT stop my mare's mane rubbing. She was/is rubbing just as bad as ever. I ended up giving her a good bath to with medicated shampoo and de-wormed her in an attempt to stop the rubbing. But all the MTG did was make her a greasy, stinky mess.
I also put it in my gelding's mane and tail and he started tail rubbing, which he doesn't normally do. So I don't know, but it didn't to a thing for the mane rubbing in my horses for some reason.
What actually has helped my gelding when he used to rub his mane was fly spray sprayed at the crest of the neck. He hasn't rubbed out his mane since I started doing that in the summer, for a couple of years now. That didn't help my mare though.
PS. Some horses just naturally have thicker manes/tails than others. For instance, John (see the horses in my profile) has the most wonderful mane and I do nothing to it at all, just occasional brushing and fly spray and it is lovely. But I've had other horses with thin, wispy manes with the same care.