captain b:
Regardless the distance a pendulum sight is accurate to, the primary advantage of a pendulum sight is to not have to estimate the distance to the target. With some bows, one fixed pin set at 30-yards may give you a X to X range that you can set the pin on the spot, but the trajectory is not as flat as some believe it will be.
You might sight in at 30-yards with one pin and then only be able to aim at and hit the same spot down to 25 yards before the shaft starts to hit too high and you have to know the distance to properly "Kentucky" the pin to spot. A pendulum, if a good pendulum and all other things are right, may be accurate from 5 to 40 yards, depending on the pendulum, without having to adjust the aim.
I have used many types over the years, from a $4.00 brass swivel pin, to a $50.00 Mason that lit up the yardage with an LED light, to an $80.00 pendulum that I could use from 10 to 50 yards with fairly good accuracy.
I know this from experience; do not go too cheap on a pendulum. The Keller was good, but to noisy for me and I did not like the narrow sight window. However, many shooters use the Keller with good success. I found the ABC Pivotal to be the best out there.
http://www.bowhunting.net/abc/sgf.html#top
The ABC allowed me to make a quick and easy adjustment for stands of different heights, and to set the pendulum to correspond with the speed of my bow.