Just a note, to measure the air flow through my MFC, I was using an independent mass flow sensor. I bought it directly from a Honeywell sensor distributor for ~$100:
AWM5101
http://sensing.honeywell.com/honeywell%20sensing%20and%20control%20product%20search?sid=1361C81FF163&Ne=3025&N=3468
The sensor is very easy to use, but I just added on some ports for power in and a BNC. If you already have a scope or a PC with a DAQ, this let's you measure flow and for much less than $1000.
