Do it yourself, takes YOU the same amount of time as using an agent..The agent asks YOU to provide to the agency, all the information that YOU would submit to immigration, if doing it yourself.
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.