I have done many shoots with the firestores, they always seem to work, but are really flaky. I had 2 cam shoot, and the displays on both units went out, could only get them back by restarting them. then another firestore the display reversed on me!!!! Talk about confusing. But, they always seemed to record what they were supposed to.
I have also done a few shoots on P2, and they were flawless in operation.
Firestores- Lenghtof recording +, reliability ?, quicktime playback +, copy time to computer slow), bulky for run&gun
P2 – reliable, little short on recording time, no playback until into FCP (unless you use the camera), copy time to laptop fast, easy to carry extra cards.
I actually don’t like having all my material on one physical drive.