Most 12V fans will work, up to an amp or 2 (your power supply will be the first limit, then the PCB traces - can't remember what they're rated for off the top of my head).
Fans are usually more efficient moving air w/o restriction, centrifugal blowers can overcome more static pressure (like pushing air through charcoal/meat/small outlet openings).
The HM-recommended delta will put my Keg on runaway fire at anything over about 40%. You'll probably be fine with a fan, depending on your pit size.
Well put, young Andy!
Remember that a BBQ needs air, and if you run it "old school" it's natural draft. I don't think "static pressure" really enters into the equation for stoking a fire (as proven in many threads here), of course, depending on your smoker size. You need to add oxygen, and depending on your setup, it really doesn't require much "fan" air to make it so. I think it's more about the PID settings with the fan/blower setup you have. With a fan, the settings may deviate a bit from the norm (of course, I could be wrong).
I think SteveCK has busted this myth with his MicroDamper design.
I'm not a ventilation engineer, but I did play one on TV.
I use a blower, but I dialed it down a bit with my design, just for the fact that with the Delta 6.7 CFM blower, I had to dial down to almost 20% max with my 18" WSM (and it's a leaky bastard). The Adapt-a-Damper uses a cheaper 5.7 CFM blower, but even cheaper would be a fan setup such as SteveCK suggests to run even the most inefficient grills.
With a Kamado style grill, I would suggest a setup to run damper over fan, and have the fan turn on only if needed.
Now, of course, if you have a beast, like a 3 tier Pro Q/WSM style smoker like someone posted here most recently, then yes, you may need a blower, and a large blower at that, depending on what size orifice you're sending the air through.