Auto_complete_field Vs text_field_with_auto_complete


I want to know which of the two methods, auto_complete_field and
text_field_with_auto_complete best suits what I am trying to do.

I have a model class called search (which doen’t extend ActiveRecord)
which holds two parameters, category_string and postcode_string.

I want my form to bind its values to these to values. I also want the
category input to be an auto complete field (after the first three chars
have been input).

What is the difference between auto_complete_field and

Does text_field_with_auto_complete support :min_chars as I can’t get it
to work?

Can text_field_with_auto_complete bind to the search class?