the arrows will be added to all menu levels, not just the ones that include sub menus.
you can edit the css and the menu so that only the ones that have submenus include the arrow.
in the menu.css file, look all instances of the following line:
and comment it out;
then in the menu, add an inline style to the menu items that you want to include the arrow on, for example:
<li class="parent"><a href="Products.php" style="background-image: url('plugins/CSSMenuWriter/cssmw0_images/arrow.gif'););">Products</a>