Is there anything physically different about the Air-O-Cell® CSI?

Yes, but very minor.

1.    The label uses a maroon color, instead of green.
2.    The serial number is printed on the slide inside the cassette and not on the label.
3.    The adhesive on the slide is completely different.
4.    The geometry of the inlet slit is narrower, and matches the geometry of the inlet slit found in the Via-Cell product. Because of this, customers using the Zefon Bio-Pump should use the Via-Cell flow indicator that came with the pump. Zefon is currently rebranding these flow indicators to specifically state both via-cell and Air-O-Cell CSI.
5.    The inlet slit size also has changed the particle collection efficiency and moved it from 2.3µm @ 15 LPM to 1.56µm @ 15LPM.