Well, not really. ‘Helper’ would be a better word. You upload an old-style template to the form and it translates most tags to the new syntax. It does not force your template to be well-formed (which is required), nor does it properly do attributes with expr: It is meant as a help for converting, not an auto-converter.
Note : especially for crufty or very-much-hacked templates (like mine was) I recommend re-engineering from scratch, from a default Blogger template, or from one of my templates. It is almost easier, and better for you in the long run.