DG before you buy anything check the iPhone apps. I have been running Digifit's software since they first came out a few years back. Have enjoyed it. I have tried a slew of others. they are all fun.
Battery life is fine. I ride daily an hour each way to work/home. 10% battery use during that time with all the bells and whistles going. Battery life is not a problem. I did a metric with it (before my accident last year) and had hours and hours battery life left when done. I really don't know what the problem folks have with iphone and battery life but I've not had this issue.
there are scads of apps available. check a few out.
I used the RAM Mount until Digifit came out with a new box mount that I really like. There are others out there. YMMV.
Best thing is if I need the phone it's right there. Has literally saved my life twice now. EMT's grabbed it and used it to call my wife. Also handy for SAG ride calls... :-)
oh and GPS, Speed/Cadence/Distance (Garmin SC sensor) HR too all talking to the iPhone.