I installed WWW::Mechanize (I may even end up using it someday), and looked through the docs:

$mech->content(...)

Returns the content that the mech uses internally for the last page
fetched. Ordinarily this is the same as $mech->response()->content(),
but this may differ for HTML documents if "update_html" is overloaded
(in which case the value passed to the base-class implementation of
same will be returned), and/or extra named arguments are passed to con
+-
tent():

$mech->content( format => "text" )
  Returns a text-only version of the page, with all HTML markup
  stripped. This feature requires HTML::TreeBuilder to be installed, o
+r
  a fatal error will be thrown.
[download]

So it looks like the call is correct.