You are paying them purely to submit the application on your behalf. Immigration will get exactly the same information they need either from the agent or yourself. An agent is for people just don't like the hastle, BUT, the agent will ask YOU to provide the information to them to submit on your behalf.
Same amount of hastle..
I did all of my wifes visas' for Australia, sure, lots of work but no less either way.
Not in Australia..I had my non imm spouse visa approved very fast online. But, I still had to mail passport and other doc's to the interstate embassy to get the visa stamp..