Here is the code to show an extra field on products.tpl in 4.1.xx. You just have to put the name of the extra field that you want to display in place of nameofextrafield.
Code:
{if $products[product].extra_fields ne ''}
{foreach from=$products[product].extra_fields item=extra_field}
{if $extra_field.service_name eq "nameofextrafield"}
{if $extra_field.value ne ""}
{$extra_field.value}
{/if}
{/if}
{/foreach}
{/if}