What's debatable about their usefulness? The word "nudge" should indicate to most people they aren't good enough to bounce things off. The nudge bar is there to stop your bumper getting scratched when or if you "nudge" something, and in most nudge bars they will do exactly that.
As for mounting lights any mounting surface can shake lights and blow globes through vibration. Bullbars, sports bar, even standard bumpers all have about the same probability of shaking globes because they are all bolt on accessories. I also refer to the globes blowing not the lights breaking as I've never broken a light by simply having it vibrate I've only ever broken them by hitting objects, I have however had globes vibrate and stop working. I'd be seriously p'd off if any driving light I paid money for shook to pieces because it was mounted on a nudge bar
You mightn't have broken lights, but then maybe you ahven't travelled as extensively in rough terrain as me either. I don't know. Regardless, just because you haven't experienced it directly, doesn't mean it doesn't happen.
All I can relate is my own experiences, and in those experiences, I have found the nudgebars and poor quality bullbars to be of limited value.
I have been in convoys where I've seen lights physically shaken apart through poor mounting. And two of those instances were where the lights were fitted on a nudge bar. One was a Nissa Navara (genuine Nissan) nudgebar. One was a Mitsubishi Triton GLX-R factory nudgebar. One was when the lights were fitted to an Ironman bullbar. We''re talkign about two different sets of IPF lights where the rivetted mount came away from the housing. And a set of Cibies where the same thing happened. All through constant vibration on corrugated and rough roads.
Bolt on accessories they may be, but the mounting structure is an all important factor in the reduction on vibration.
It is my experience that a well designed bullbar with well designed mounts will move and shake far LESS than a poorly designed one. And in my experience, the Nissan nudgebar is nowhere near as solid as an ARB bullbar. How can I prove this? All you have is my word. When I bought my vehicle it had the Nissan bar fitted. When I travel to one of my favourite hunting spots, I often head down there on a Friday night after work in Winter. The track is about 20km long. The IPF lights on Nissan nudgebar used to shimmy and shake on the drive in. Hardly a good sign, and in my experience off road driving, evidence that the light is vibrating in relation to the chassis - the mount on which the light sits is not strong enough to prevent the light moving. Since fitting the bullbar, that same track and the shake in the lights has completely disappeared.
Sure, a nudgebar may save a bump or scrape in a carpark - and if that's what you need, then fantastic. But it will only prevent scratches etc in the centre area - anything off-centre will still hit the bumper. But some of us need something more substantial than that.
Perhaps I should have said "in my experience, their usefulness is debateable for anything more than light duty excursions off road".