Claims that something is “Myford size” are mostly utter nonsense (unless you find genuine originals).
I have mostly Bison holders (details below), and original Dickson seem to fit fine as well.
As for all the other offerings (from the model engineering trade as well as ebay),
they can also be made usable providing you are willing to modify them.
Carbide cutters make it easy on my milling machine.
Some are easier to modify than others…