For those who dont know, the JoJo Rage is based on JoJo's RM open celled race kite. The RM has been one of the top land kites for awhile now, and the kites characteristics were transferred to the Rage and so has certain characteristics as it was designed to fly on handles and is now used on a bar.
The third line that is attached to the bar, as it is set from the factory, is not for sheeting, it is attached directly to the brake lines, and so is only designed to brake the kite (evenly on both sides), or as a safety. To set up a sheeting system a series of crosslinks are tied to the front power bridle lines and this is what changes the kites shape (not the angle of attack), effectively sheeting it in or out. Contact the North American distributor and I am sure he'll show you how to do it.
Both the 10 and 12m are tanks, they have tons of pull, even in light wind.
Slow turning speed is a relative thing, I would compare the 10m Rage to my 10m 2002 Fuel for turning speed, though to a 14m - 16m Fuel for power.
Both kites are pretty stable, I have flown them in winter mountain winds (on telemark skis), which are very gusty and full of holes and I haven't had a problem there. They dont collapse as easily as an open celled kite, cuz of the pressurized cells. Though they will fold in the middle, clap the wing tips together and re-open, which can take some getting used to.... but that is only with extreme gusty conditions.
Overall I think the Rage is a pretty good kite, once you learn how to fly it, they are moderately different from LEI's. My only beef with them is that some times they are hard to pre-inflate with the small openings, this can partially be remedied by opening the zippers close to the trailing edge that are designed to help deflate the kite. Once partially inflated they are easy to deal with, and it's still quicker then pumping up an 18m to 20m+.
Oops... sorry... didnt realize I was typing an essay... but hope that helps