It's not either or. You can do both. They're not exactly official cats. They reflect what's actually there in the 7000 groups I looked through.
To you the exact kind of radio group you are is important and you can use keywords and tags to define this. To anyone uninterested in radio it's just one big lump with a massive following that buries niche interest groups
Being able to exclude that entire category would be very helpful. The cats are broad on purpose and based purely on large group numbers.
A search presumes you have a good idea of what you want to find and that the keywords or tags you use match the ones the group owner used.
Cats and searches are like catapillers and butterflies. They do different things well.