World-wide, about 87% of all applications are done through an advisor or professionally prepared, *BUT* if you've got clean noses and your case is straight-forward, there's usually no need for a non-visa national to engage an advisor. Some do because they don't have the time, or don't know the rules, or just want to outsource the stress to someone else. Others need an advisor because there's a genuine problem. But for what you have laid out in this thread, it would be overkill. So keep your noses clean
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In hammering out your strategy, it might be useful to note that they are still allowing in-country switches from visitor to UP as long as the applicant has the requisite cohab prior to any removal actions.