I've got one of these and they're pretty slick. You'll hear a lot of debate on whether they're worth it or not, but I guess that is really up to the individual.
My current set up is the TLD 7855 short sleeve shirt, and D3.
Everyone's body is different, but this combination works well for me. I'd tried other helmets that I've seen other people wear (Giro Remedy, Down-o-matic), but I couldn't get the adjustments to give me the range of motion I needed for really steep terrain. I must have a short neck(?).