Here is an excerpt from one of them.

"When you get hot and begin to sweat - especially if you are wearing a shirt with no sleeves - the armband begins to slip off the arm, forcing you to yank it tighter. It's not a good design at all. Plus, the armband is not very long, and males with average to larger biceps will find it very constricting. I can't imagine a sports armband that doesn't stretch, but this may be just a strongly ingrained personal preference."