I wouldn't personally put rusk in a burger.
I don't know what this commercial formulation tastes like, but do know that I don't need half their ingredients in a home made one, theirs is done to give a shelf life which, presumably, you don't need.
I'm sure that if you can describe the taste profile, others will offer help.
However, I would point you in the direction of
this burgerby forum member Oddley - it's been received very well by all members of this site.
You could maybe start with this, and then adapt it to your taste?
Phil