I own a 2013 12m and 16m NRG.
Liquid Force has a video on tuning your bar and lines, it helps ALOT.
I hated my 16m until I changed the bar and kite settings, now I love it. For me, I went with lightest bar pressure (fastest turning) by setting the rear bridle attachment closer to the wingtip, lightwind setting on the rear lines via the knot labelled as such, and then moved the bar line attachment down to the middle knot. I fly it like this in virtually all conditions altho I've considered moving down a knot on the bar in light winds as I like strong bar pressure. I really prefer the way the kite turns on its wingtip though so I won't touch the light bar pressure/fast turning setting, especially since there are other ways to get bar pressure. 16m Kite flys like a champ now
I've used it in 12 mph-28 mph winds (the 28 mph was by accident, surprisingly it performed really well and stayed smooth/controlled - some big boosts that day
I will not even bother trying to use it if its below 12 mph, its lighter wind not ultra light wind (eg, its not a FS or Chrono).
In terms of relaunch, I've never had any real issue but it depends on skill level with the kite I guess. Others have constantly complained about relaunch online so you are not alone, but I've been able to get mine in the air in 8 mph winds fairly easily. In sub 15mph winds, I usually just hot launch or reverse launch the kite - dangerous but if you prep yourself for the yank forward you can get away with it (I've even done this for an emergency low wind waterstart).
Otherwise, get the LE down facing the water like a wide "U", grab one of the rear lines (you may have to go past the bar float coated leaders, but avoid having your hands on the lines as much as possible - having your hands on the lines is dangerous as the lines can slice into your hands), hold pressure on that line as the kite swings round to that side, it will start rotating onto the wingtip. Once on the wingtip you have to manage letting go of the rear line with switching to using the bar without the kite simply falling back to its LE face down "U" shape. If its super low wind, you may need to climb the wind window gently by occasionally sheeting OUT as you park it parallel to the horizon. The overall difficulty of relaunching the NRG vs other kites imo is that the flat canopy/tank like structure requires more extreme input in order to get the kite on its wingtip relative to a lighter weight/ open C kite style.
23m lines - if you use the 7m line extensions it turns like a PIG. The extensions are only useful if there is a strong wind gradient (strong winds at 30m and weak winds at 10m of altitude) as the ktie likes the 23m. It DOES pull like a Mack truck with the extensions but you will find yourself nipping the top edges of the wind window to avoid the kite dropping below 10:30.
The kite is flat out heavy. It needs to be fully pumped up or you will get alot of problems. Inversions in particular are a sign to me you are probably under-inflating your kite. The kite has a stiff structure when fully pumped up and rarely inverts, only inverts on me when I flag out on the lower center line.
I usually pump up my 16m in two stages - I pump it until it starts giving me slight resistance on the pump (wingtip still folds easily). Then I close it up, park it while I do other stuff, come back and finish pumping it. It takes a few minutes for air to fully equalize between the struts and the LE for some reason and that is slowing it down. YOU CAN TELL if you need to do this by feeling the struts, especially the ones on the wings, and feeling the LE. If the LE is rock hard but the strut is much softer - you need to let it sit. If you have alot of beach to play with, I've noticed flipping the kite and walking around with the kite upside down in walk/transport mode tends to equalize the pressure much faster than letting it sit on the beach. Once I have the struts hard, the kite stays that way for 6 hour sessions, the valves just get tight once you start getting air into the struts for some reason.
Overall, I think the NRG is a great big guy kite for 15mph+ winds because the heavy structure will offer you alot of support when you are riding, especially for boosting. I do not think its a good pure light wind rider kite; the Solo, a Zero, or a foil would do a much better job in sub-15mph imo. I know the brands like to cross market those two segments but not every solution works both ways.