What garbage! Just create two applescripts to do the same thing for free! Here's the code:
Filename: "Hide Selected File Extensions"
Code:
tell application "Finder"
set the selection_list to selection
if (count of selection_list) < 1 then
return
else
repeat with the_item in selection_list
set the extension_state to get extension hidden of the_item
if the extension_state is not true then
set the extension hidden of the_item to true
end if
end repeat
end if
end tell

Filename: "Show Selected File Extensions"
Code:

tell application "Finder"
set the selection_list to selection
if (count of selection_list) < 1 then
return
else
repeat with the_item in selection_list
set the extension_state to get extension hidden of the_item
if the extension_state is true then
set the extension hidden of the_item to false
end if
end repeat
end if
end tell

Just put both scripts in your "~/Library/Scripts/Applications/Finder" folder and enable the script menu. Done.