Tom - since 2006 all OR SLE kite bars and SLE kites, Ones ( 2006 & ‘07 ) and Rise kites ( 2007 through 2011 ) are designed so that the larks-head loops at the ends of the 4 lines are the same length when the depower trim line on the chicken loop is set to full power.
The kook-proof connector on the rear steering lines is the same for Ones and Rises too.
So newer OR SLE bars will work on a 12m One, just try to get the widest bar you can, 60 cm if possible, as the One turns pretty slowly, especially with a narrower bar.
Hopefully you have an experienced kiting friend riding OR kites that can show you his/her kit and help you get it figured out. It’s hard to get this kind of stuff figured out on your own just with the info on the internet.
You will also have to sort out your leash configuration ( what happens when you release the chicken loop and the kite is constrained by the leash ). The first SLE bar came with an line to leash to one of the front flying lines for novice riders, to depower the kite more than leashing to both front lines, by attaching the leash to the loop on the end of the trim line. Ugh, it’s hard to explain this stuff in writing, best to get an experienced rider to show & discuss the pros & cons of leashing to single or double front lines ...
Hope this helps.