Pinwheel...I agree <img src=icon_smile_big.gif border=0 align=middle>

Like I said earlier....why take the chance...if you don't have to? And I agree that they are many times used as a band-aid for a setup that is not tuned well enough for fixed heads to fly straight.
If you have your bow tuned properly(as many here do), and have the KE, go for it. You'll probably be ok. But to me it's just not worth taking the chance(no matter how small).

Rangeball...in the scenario you describe...it really makes no difference. A double lung with a fixed or a mech is just that...a double lung.
What I look at is, not how both perform on a perfectly placed shot, but a poor shot. That's where the differnces(advantages/disadvantage) actually show up and make a difference. If I knew all my shots would be perfect, I could buy the cheapest head I could get...still wouldn't matter...dead animal.