I've flown a few times with various devices and never really had any problems, my experiences have been similar to the above, however...
I do know of someone that lost their mod in the UK, they gave the option of binning the mod or going home with it, that's it. They were asked if it could be kept or posted back and the reply was we 'will send it back to you if you have a postage paid, addressed envelope with you'. Obviously this was an international flight originating in the UK and it was quite a long time ago, I don't know about US domestic flights.
I usually pack my P16 dismantled in my luggage for the hold and I have an old screwdriver I don't care about for taking on the plane, at the least it might be worth taking an envelope with you. Beats gambling with your P18, no matter how small the odds of losing it are..