I had Core ESP bar that was adjustable and it worked really good for both my GT 15m and GT 9m. Only problem was that I would usually forget to switch the bar from the outside setting to the inside setting since 80% of my riding was on the 15m. The result? I had a blast on the longer bar setting with the 9m and never realized what I had done until I came in and rolled the bar up.
This experience led me to buy my next kite, 13m, with 55cm non-adjustable bar to use for both the 13m and the GT 9m that I kept. The result? Works great! Jumps and loops so easy yet still is very stable with hands in center of bar. Kite has adjustment to turn slower but haven't even tried this yet.
Is anyone else just using one bar for everything? Sure helps when new bars cost up to $500 now.