I just did my second vehicle yesterday with D300. And it was actually the first time I went straight to D301. It was my nieces car and she's a college student, so it didn't need to have the ultimate gloss or anything. It was quite swirled, though, with 70k miles on it and I talked her into getting a nearly-new finish. Turned out great!
My experience thus far with D300 has been on two GM vehicles (Suburban, Saturn Aura) and a 5-yr-old repaint. With 6 section passes (4 heavier, 2 lighter) and slow arm speed, I was able to remove all defects except some deeper water spot etchings and RIDS that were hard to see on the metallic paint on the Aura. The paint finishes down pretty nice for a compound and has very little dusting (I use compressed air to clean it after each panel or two). I'm also able to get by with very little taping. I actually didn't have to tape anything on the Aura. This is huge, because with M105 and a more aggressive pad, I need to tape A LOT and it dusts everywhere and doesn't finish down quite as nice and may need an extra buffing step.
I'm using the D300 in an exterior package that I recommend for daily drivers where I'm not trying to get every defect out. I call it the "silver" package. It's D300, M205 and PO85RD on most vehicles, though I have several other products if those aren't ideal. I used this process on my Suburban after wet sanding it and it's unreal.
I wrecked two of my three MF cutting pads and made it over the Aura with one 6" pad. It can be done, but takes a lot of cleaning and it dusts a lot by the end. Much faster to have at least 2-3 pads!