David,
Aside from the filtration that the powered respirator provides... there's a side benefit.
The air flowing over your face pretty much assures a fog free shield, and a pleasant breeze while turning.
On the rare occasion that I use a regular (Bionic brand) faceshield, I really miss the air flow. So I use the non-powered shields only when I'm away from my own shop (in a class, for example).
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