If it works for your existing pocket door, then it should work for additional pocket doors. Normally, exterior doors are an upgrade from interior doors, and so you should be fine, as long as it works with your door thickness. It does not work the other way, with substituting interior doors/hardware for exterior, which was what had been done in our garage. We had to buy a new exterior door to replace a cheap interior door that went from the garage to the patio.
Overkill is acceptable, underkill is not, and the two should not be confused. Does your designer know that you already have this door hardware inside your house? Sounds like you need a different designer.
Lars

I think it's for door thickness 1-3/4" which is a typical exterior door thickness. They make one for 1-3/8" thick doors, too.