So...style thing...

1 == $subform_element_object->ele_value["simple_add_one_button"] is an implicit way to get the true value set, because it returns true, but this strikes me as less readable than:

(isset($subform_element_object->ele_value["simple_add_one_button"]) AND 1 == $subform_element_object->ele_value["simple_add_one_button"]) ? true : false;

That version is more explicit about what is going on I think.