I used to have a tripod with center column. Then I finally bought RRS TVC-34L and have been using it without center column. That was until last week, when I finally decided to order a center column for it, and I received it yesterday.
The RRS center column seems pretty sturdy and doesn't wobble or anything but it does add more contact points, and thus possibly reduces stability by just a bit. But for shots like portraits, real-estate interiors, etc., the convenience of a center column for quick height adjustments cannot be neglected. It was just painful for me having to adjust the legs every time I wanted to adjust my camera height by a bit. That is the reason I finally decided to add the center column.
So, my plan now is to use the center column for all my portraits, real-estate, etc., and to remove it for all my landscape and wildlife/bird shots.
