I've used it for a long time with all sorts of horses, and it blends really well with other modalities.
It's system of bodywork, groundwork, and riding exercises that teaches horses to think rather than react and sees balance as being interconnected physically and mentally.
The Tellington TTouch (as it is now known) is really useful especially as it looks to find the source of behavioral problems (ie tension or pain in the body, fear) and address that rather than label the horse "dominant" or "disrespectful" and deal with as such.
It can seem a little different at first, especially as it doesn't really fall into a category, it's not Natural Horsemanship and it's not traditional, but the changes that horses can have are pretty remarkable all through non-confrontational methods. Their website Tellington TTouch Training™
has more info.