I have been using the 30M Naish V4 for over a month now. I bought the kite with my own money and I have to say that I am still very impressed. I have found that the wind range for my weight and ability (75 kg) is 8 - 17 mph. The kite will fly in 6-7 mph. 8 mph is enough to plane, but not stay upwind. I need about 9 -10 to stay upwind, but jumps come at 12. I really like the kite in 12 - 15. That may sound strange to some of you. You are probably thinking, "I can ride my 20 in that amount of wind." True, but if the wind is inconsistent (as light wind often is). What are you doing during the lulls? The 30M V4 will stay up in the air, when most 20M kites are on the water. I saw this happen a number of times. The V4 was still flying when the following kites went down Aero II 20M, X2 20M, X3 16M, Gaastra 25M Phoenix, Gaastra 19M GXR, etc. I found that I was able to stay on plane when the other guys were sitting in the water waiting for the wind to come up.
Relaunching - I can't give you much help here. I have relaunched the kite many times, but it was always in waist deep water. The kite is a cinch to relaunch in shallow water. I haven't had a chance to try it in deep water yet.
Jumping - Solid, gliding jumps. Less pop than my 20M, but I can jump when I would be just barely planing on my 20M. When the wind picks up over 15 mph, I found it is better to go in and rerig if you have time. You can still jump, but it is so difficult to edge against a kite that large that jumps tend to be low and fast.
If you weigh over 175 LBS and you often kite in light wind, consider this kite. If you are 150 - 175 and kite in light wind consider the 25M.
One more comment, when I talk to other kiters at my local spots many are afraid of a 30M kite. They think that they are going to be launched a hundred feet high. I always tell them that there is little difference between a 20 and a 30M kite. I tell them it handles like a puppy dog. I would never take the 30M out in squalls or nasty conditions, but if you respect the kite and use it in light conditions, it is your best friend. Thanks Robby