Droid + HRM

photorific

I've been toying with the idea of getting an HRM, but also don't want to add any more gadgets to my arsenal than necessary. Decided that since my phone is with me on all my runs, it made sense to find something that is compatible there. I have the Droid Razr, and have seen 2 straps that seem to be compatible - the Zephyr HxM, and the Polar H7. Reviews seem to be mixed for both, so thought I'd see if there was anyone here that had feedback about them or even if someone knows of/uses a different HRM?

edit: I tend to like the CardioTrainer app - bonus if one of these is compatible with that...