Just be aware that at the moment Strava is only capable of using HR data from a Garmin device , if thats part of your plans.
I use my iPhone as a gps tracker only , in the back pocket of my jersey.
I was using a topeak mount but it was a bit clunky, didn't feel that safe either way up there on the bars
If you are looking for specific and sturdy mounts have a look on here.
We use their iPad mounts at work in constant motion situations and they seem to be the best available.