Brilliant mod. Just did this a couple of weeks ago on my 12m Xbow. I did opt for the new length of bridle line though. Â£15 later and the mod really does change the bar pressure, I used to have to come in after about 40 minutes with forearms like popeye! But since the mod I can stay out for 4 hours and not feel the pain. The Xbow turning speed has markedly increased from stock making for a nice quick turning kite even in low winds and in a back to back test compared to my Flexi Atom makes my 12m Flexifoil Atom feel like an ocean going liner when trying to turn the atom. The depower has reduced a little though. Letting go of the bar means the kite now parks above my head. Albeit with little pull (but still less pull than the atom). To summarise a sweet mod, and worth the half an hours work to do. A few tweaks to the bridle should see the depower back but to be honest I like it as it is. As other posters have said the new pulley doesnt move much up and down the new bridle, maybe a couple of centimeters so using the joining trick should work.
I did read on one forum that some guys have had their bridles snapping when they have tied the two old bridle pieces together as in this mod but as an engineer I can only think that they must have had either sticking pulleys or worn original bridles as the forces transmitted shouldnt have increased by using this mod.