I have tried a tecbuk brush too and thought it was great at first, seemed to fly over the glass. I then put my gardiner medium dual trim back on and realised the tecbuk wasn't that quick at all. There was a noticeable speeding up on the glass, a bit less drag, with the gardiner brush. I got a bit caught up with the hype Re tecbuk brushes on another forum. Different brushes suit different people though so I wouldn't knock anyone who thought they were the bees. Compared to most brush makes tecbuk are better but in my opinion just not quite as good as gardiner, not far off though. If they did a sill brush I would give it go to see what it was like.
What type is it James...mixed, boars hair etc?