I have done it on both my 80D (bought new by me) and a SH 5D.
The 5D was much cleaner than the 80D, despite the fact that I know the full history of the 80D and that I never left it without a lens or body cap. I'm guessing the 5D's weather sealing kept more out.
What I found very useful was to connect it (them) to my PC and set up a studio session. Every shot I took was imported with huge contrast added, so it was immediately clear when there was dust.
You can only use each swab once, and I went through a pack trying to ensure I got all the specs and that I didn't leave any drips of fluid on it - which I did several times.
There were definitely times I really wished I hadn't started doing it. Especially when I was getting towards the end of my stack of swabs.
But I'm pleased I persevered.
