It always matters where you download mods from. You always want to trust where you're downloading from. With that said, I have found Play With Six useful for adding and removing mods to my ARMA game and updating; it makes it easy to manage the game and its mods. You can find it by doing a simple google search. I think Steam workshop will work similar to Play With Six in that modders can develop their mods and update them and steam will push those updates out to the users. It will also allow modders to put prices on their work. So, yes, I think the Steam workshop makes it easier to download and install, while other sites or repositories will be a little more difficult.
