Hi Javier!
This plugin only register new tabs for WooCommerce, and does not change any styling setting, because the plugin does not responsible for styling.
If your theme works well, all tabs including the additional tabs have the same font.
If your theme change the fonts exclusively for specific tabs, that is a theme issue, because the theme does not support additional tabs.
Your theme developer can modify the theme to handle the design of all tabs (including additional tabs) consequently, or you or your site designer can apply some custom css styling to change the font on the other additional tabs.
I hope this information is helpful for you.
Peter Rath
WebshopLogic