I don't post here anymore but I have been following this thread. I received my AR1 on Dec. 29th and had many issues sorting the brake out. Finally the TRP 550R was what I could get to work properly. My wheels really make this a challenge as they are over 28mm wide. Any how, someone said a while back they wanted to try the bontrager unit. It will not work as bontrager has its own proprietary mount setup and that is why you see three bosses on the fork and if anyone has seen the BB area there are three as well. The bontrager uses one of the normal direct mount bosses and then a centrally located mount. However, if someone still wants to give it a go I have one sitting on my box at the moment that you can purchase.
Also, my lever is extremely stiff but I rarely need the rear brake and if I do (think descent) I am in the drops and do not find it hard at all to use as leverage is increased at that point. Maybe SD's method of file would help, but I am not keen to mess with a working setup.
Lastly, I know there is some recent issues about weight and I know mine came in at a respectable weight. It is no 56 or even a 54, but my 51 weighed 1071 with hanger and water bottle bolts, but minus cable stops.
The heavy bit was the seat post, but I figure it could have been heavier if not for the method of design. Also this includes the clamp mechanism but not the fixing bolts.
The fork was a downright WW part at 295g cut. Shown Uncut below.
Finished pics of the build can be seen over on ST's home page. I originally built it up with 10spd RED and complete weight (pedals, 500, w/o bottles) came in at 14.9.
I have since added Ultegra Di2 and Elite Crono CX bottles and as it is shown in the feature it weighs 15.6. To be fair with the crono bottles mounted it weighed 15.2 with the RED group and Deda stem.
I hope the weights and brake information is found to be useful.