One thing to be aware of, AC treats PHR/portals diffently form some other programs, and allows them different capabilities. So if you look and see what PHRs AC is integrated with, Updox is not on the list. Practicom (which has been taken over by another company I believe) and Microsoft were the only two on the list the last time I checked.
I'm not saying that you shouldn't use Updox. I use Updox and like it very much. It's quick and easy to use, relatively inexpensive, and has some convenient capabilities. Though of course they aren't perfect.
For example, on the PHRs AC allows them to automatically upload lab results once you sign off on them (at least Practicom said they could with AC. I didn't contract with them.) AC does not allow Updox to do that.
