I first tried 3M SMR about 9 months ago on my wife's new black civic that we got from the dealer full of swirl marks. I was nervous about making matters worse, but I just dove in (hell, it was the wife's car).
I started on the front fender on a small section and wiped away a portion after trying it for a short time to evaluate how well it was working, then kept repeating this section till I got a handle on how well it was working and when I was finished. Once I got the hang of it, it got pretty easy, so don't be afraid to jump right on in, I found it requires buffing longer than it appears that the 3M is still working.
I'm also embarassed to say I used a cheap Sears polisher to do the job! Car lookd great when I was done, didn't take long to get most of all the swirls out.
BTW, I hate how quickly those swirls come back.