BD, quite a few of our cbt/das students have nitros.
I'm not that familiar with them but have also read the press blurb.
What you want is a lid that is safe, comfortable & affordable.
If its plastic then it has a usefull life of 2-3 years
If its fibre glass or one of the fancy tri-composite thingys then its useful life is 4-5 years
OR UNTIL YOU DROP IT-whichever comes 1st.
As long as it has an EU standard 22-05 or BSI standard blue(type A) or green (type B) sticker then its OK.
Generally speaking, all lids are made the same way-hard outer shell, energy absorbing inner polystyrene liner, comfort foam liner, material covering.
The cost differential is in the QUALITY of materials used (& the Tri-composites are hand laid up)
There is nothing to my knowledge that states the more expensive helmets are any safer than a "budget" lid.
They may be more comfortable & last the test of time better than a budget lid.
Its like the Rolls Royce versus Skoda thing, both will get you where you want to go-one just might get you there less stressed out than the other
and FINALLY-the more vents it has the noisier it gets-the deafer you get.Find some one who has one & ask how noisy it is-then invest in a set of custom made earplugs-£ 80.00-last for about 5 years.