The T&Ks are much more stable, you are attaching to a much larger area of wall, you are likely to get movement on an L bracket of that type, unless it is really heavy duty. They also have the advantage of being very easy to adjust to get your mast perfectly plumb, the L shaped bracket is often very difficult to get plumb, but you obviously managed that. :)
Thanks for the advice. The dish has been up for more than a year now and only had to adjust its elevation slightly once in that time. Trying to get the bracket plumb was very difficult especially on a roughcast wall but hammering bits of wood in behind seemed to do the trick.
It's in quite a sheltered location so the L bracket seems alright for my needs.