Teff hay is one of the most over-advertised - absent of hybrid bermudagrass, that there is. There is nothing magical about it - it is a warm season grass hay. Actually, it is one of the more expensive hays to grow - alfalfa is much easier.
Glowing claims about the wonders of a particular type of hay are baseless without a forage test to validate them. Then when you have that forage test, that test is good only for the hay tested in that lot, baled that day, on that farm, and on that particular field. The quality of a particular hay is paramount to the quality of the soil underneath that hay and is not endemic to the species of grass itself.
Buy all your hay from producers who test it! You don't go to the feed store and buy Johnny's Wonder Feed with no label and full of mystry ingredients, so why do you buy hay that way?