I decided to pick one up after seeing the video. It's a pretty decent arm band that seems well constructed. Phone slides in and out pretty easily and it stays pretty secure around my arm during my runs. Unless you have really scrawny arms, you shouldn't have a problem with the fit of the arm band.
Since it's made from neoprene, it's going to get pretty hot and sweaty underneath after a while, especially if you're doing anything aerobic. It's a good idea to take it off after your workout and lay it out to dry off. Probably wouldn't hurt to toss it into the laundry every now and then so it doesn't get too stinky.
The combined weight of the phone and armband isn't too bad, but I find it's noticeable when I'm running. I'm probably going to alternate wearing it on each arm for my runs.
Despite the speaker cut out being on the opposite side, sounds the phone makes are still pretty audible even at half volume