I have a Thomson Elite on my Prophet and it allows you to slide the seat fore and aft on the rails. I use the setback seatpost because I didn't feel right with my knees essentially lined up over the pedals but I was out of adjustment space and couldn't move my seat any further back. Now, I'm able to set my seat so that my knees are just aft of the pedal spindle and all is well.
For my money, Thomson may make the best seatposts on the market.
Mike