I have developed the habit of offering the Headstart option to my new trade mark clients. This is an effort to smooth the way with IP Australia. To date, I've only experienced courteousy and efficiency from the staff at IP Australia.
There are detractors. Some say that the inability to prepare tailored class descriptions is restrictive. It would be, were it not for the accommodating staff. If I need to tailor the description, I simply email the new description to the relevant examiner with a request that he or she amend the description accordingly. Provided you're not trying to add unrelated goods or services, chances are that you can get a decent description on file. My cynical side might think that many practitioners' avoidance of Headstart is simply a way of generating fees through searches and responding to adverse examination reports. I trust that's not the case.
One of the reasons I offer the Headstart option is that examination is carried out by a person who examines trade mark applications for a living. As a sole practitioner, I have to deal with a wide variety of tasks and could never develop that level of expertise. Not only that, but the official fee is only $90 per class. That's a lot cheaper than contracting the search out.
So for now I will continue to offer Headstart in spite of the naysayers. I'll let you know (discreetly of course) if I have a bad experience.