+1 for Dan's comments, PH. I have two T-bars on my Raven, as shown in the photos below. The upper one has the shorter extension (55 mm), and holds my Rohloff shifter on the right side, and my bell on the left. I have flipped the T-bar so that its extension is parallel to the ground (not so easy to see in either photo -- sorry!)
The upper T-bar is also canted about 30° towards the rear of the bike. This allows me to grip the Rohloff shifter more as i would a doorknob -- that's more comfortable for me.
The lower T-bar holds my Arkel handlebar bag. In these photos, I've removed the bag, so that you see only the brackets which support the bag.
These accessory bars are very well made, and also serve as spacers on my steerer tube. Because I use drop bars, the shorter upper bar is essential, and as mentioned, adjustable for a more comfortable placement of the shifter. The lower bar lets me lower the weight of my h/bar bag, and also keeps the top of the bag just below the height of the bars, so that the beam of my headlight (removed in these photos) clears the h'bar bag with plenty to spare.
Hard to imagine my Raven without them -- they're an integral part of the bike, not really "optional" as the tag "accessory" suggests.
Hope that's helpful,
cheers, John