Thin, light weight, compact. Not a clip on. Simple counting steps, tracks time, and you can set stride length. Fits anywhere (in pockets), doesn't have to be vertical. I put it in my workout bra and don't notice its there. Far better then losing it off my shorts as I have done many a time.
Should fit snugly in a pocket. Pedometers are great for showing your degree of activity. If you don't get 10,000 steps a day, you should cut back on calories. A good way to gauge your fitness vs food. They are the best for setting, and sticking to a goal.