No, you dont HAVE to purchase the add-on.
SLP is already working properly. ( see screenshot and steps I took on my search of your site)
the base SLp will search more then one country if you have the settings established as suggested in above. (” search settings to be “worldwide” and not on one specific country , also set the results search to a large number under settings/results) See the docs site about both of these options”) If you do not want focus to only be Aiustralia set the zoom level accordingly, see MAP panel settings
EXP add-on allows you to have additional settings such as a drop down selector by country if you think that will benefit you. Right now it appears that you have no results displayed at start up and the Australia Map as your center map at…I am not sure what your settings are.
Set your radius under results settings higher. Also your drop down box for radius for the search box is default of 10 miles, if you are not using any add-ons you might want that to be higher. See radius behavior and settings
Fotr instaNce, I went to your url, I typed in Belgium in the search box, the location marker went to Belgium but no results found, well, that is because the default radius is 10 miles and the center of Belgium, compared to your locations in Belgium is more than 10 miles apart. When I selected the radius as 100 miles and reloaded search using simple belgium results were shown see attached screenshot.
If you want the site to be more intuitive, you might want to have Experience add-on or Premier. (Premier also allows user to have a Country address guess)
It is up to you or your client , the other options is to have radius default as a larger number or with experience add-on not rely on radius behavior.
Review the various docs site posts to determine which outcome would best suit your purposes.