I have a Forcefield protector like the Pro L2, its a couple years old, so may not be the exact model. Looks the same though. I love it, pretty comfy, I know it works when I've been run over mini racing. After my collarbone this year, aside from dialing it back a bit, I will be headed for an air vest in addition to my Forcefield. I don't want to try to cram more stuff inside the suit than I already have. All the big guys are going for the air bag stuff, and the vests seem to be pretty good.
Is the chest protector worth it? Not until you need it! If you can fit it in your suit, why not? I wouldn't worry about the heat, 20 minute big bike sessions and 15 minute races. I doubt you'd notice much of a difference. If you were taking it touring, something more to think about. The cost of good protection is nothing when compared to even a minor injury. I could have picked up any Dianese suit, the best boots and gloves, and had money to party with what I spend on this damn collarbone.