I had Triumph's own "off road" silencers fitted to my Thruxton. The one thing I really didn't like when I rode the demonstration bike was the lack of any sound. The off road pipes make the bike sound like I think a Triumph should sound.
What I like about them is that they look exactly like the originals so don't alter the look, which I love, and they are genuine Triumph parts! They are also cheaper at £300.00.