Hi Da11as,
The bars are very well made indeed - up there with any premium bars ive had in the past so no issues there at all, ive been super impressed with all the Light Carbon stuff in terms of quality.
Im not a massively powerful rider, so I can't comment on stiffness, other than to say they feel absolutely solid to me - but ive never been able to flex any bars that ive had!
The included mount is perfect, I just decided to put the titanium one on there to really finish it off - it is solid as a rock - ive ram it with a light underneath and had no problems. The 3 bolt fixing makes sure it is very secure under the bars.
Im just not a fan of the upsweep angle on the top of the bars - thats the only reason i changed, as I think they look fantastic and the quality is excellent.
Hope this is of some help to you.