The biggest thing I like about the button hollers is that they are simply simple. You set your adjustments or put in the cam, set the material where you want it, lower the presser foot and go. The button holler starts at one end and makes the entire button hole in one step.
The built in ones on all the machines we have is a multi step operation that I have never been able to make work.
And just for the information .... All the cam style button hollers I've got are made by Greist. They're just marked with other brand names. The non cam ones with the wing nut adjusters, I'm not sure of.
Joe