I had this one for my OG Droid, and wasn't a fan. The straps bunch up in the clip. I ended up buying the TuneBelt arm band for my Bionic, with an extender strap, and am much happier with it. I still occasionally have the issue of the straps bunching up in the clip, but it's not as bad.
Just an update on the armband I bought. It's pretty nice and fits my arm, which bigger than your average arm. It's comfy as well. It holds the phone with the extended battery pretty snug, but won't fit with the otterbox.
I haven't tested it out at the gym yet, but it works well for jogs so far.