I Really enjoy my Mares M-1, it's got an easy to read Bottom Timer mode, a constant on light mode for night dives and using AAA batteries they are easy to keep a set of backups in my save-a-dive kit.

The picture probably describes it better than words - you can either tie the ends, or leave them loose as I did which makes them adjustable. Note the knots at the ends of the bungee to prevent it from pulling out - the second knotted area gives you something to pull on even if you have gloves on. I considered melting the ends of the bungee, but I kind of liked the soft frayed look, so I left them "as is."