First off, there is an update on the release date, it will be the third week of September (US release, don’t know about other countries yet). It will also be aired on the Disney Channel at some point after that.
The original review is very long so I’ve clipped out the bits that are about Billy and his performance:
One of the film’s genuine strengths is the natural camaraderie that’s exhibited between Billy and Allie, courtesy of the relaxed and natural performances of Billy Unger and Sammi Hanratty, both television and film vets who are clearly comfortable on camera. Neither Hanratty or Unger particularly convinces as action heroes, but then that’s not really the point of The Lost Medallion. The real intention here is to share their adventures as friends who learn valuable lessons and who become better human beings along the way. They are remarkably convincing as friends and they completely sell the idea that they would go on such an adventure together. Hanratty plays off the vulnerability quite well, and she becomes even more convincing as the film unfolds. Unger also does a nice job here, though his character is a bit more stock in nature.
There was a space at the end of the page for people to rate the movie, 71% gave it 4 stars (the maximum), nobody gave it less than three.