Replaced OEM Tekro calipers and much prefer the braking action, feel and looks. Install was straightforward, they do fit Conti GP 4 Season 28's. take your time adjusting them, and you will be rewarded with a firm, responsive feel and great stopping power.
The Ultegra is the 105 caliper with a stiffening frame added, not sure there's much difference, but given the minor costweight delta, the Ultegra seems worth it. And they look good.
Bought these as an upgrade that replaced the older version of my previous Ultegra brakes. Overall seem much better improvement and better stopping power than the older version. Also look better and almost looks the same as the dura ace but at a better price.