Traveling in the last few months, it's been sort of 70-30 (no search - search) as to whether they stop me to look through the stuff. I DO tell them as I hand them the bag that it is recording equipment...seems to have cut down on the times I get the full search. Most of the airports I've been through, the TSA's seem to have a familiarity with the equipment used for recording, judging by the decreasing numbers of questions I get. They are most concerned if they are unable to see through something on the scan (e.g., lead batteries). I have yet to have the need to pull out the MSDS; but I'd still have it with you!
FWIW, the TSA's seemed to be most concerned about my shoes and the Leatherman's tool I forgot to take out of my bag (went back and put it in my car). Give yourself extra time and just be polite: seems to go a whole lot easier that way.