I have a HGU84, dual visor,CEP kit, flex boom etc. etc. Haven't had it a year yet but very very impressed. I got the standard liner but some of the other slaves at work have also bought HGU84's in the last few months and went with the 'custom liner' - i think that is what it's called- bloody neat & not a lot of difference in price. I bought mine from Gibson Barnes - it was a surplus military helmet - they get orders from the military then if someone washes out the helmet gets returned. Saved me $100 bucks but wld probably just go for the brand new next time. Wasn't overly impressed with the finish of the bone dome, couple of holes on front profile which hadn't been filled in - maybe from the face shield mount or something to to with the original single visor mount. I used some extra 'fillers' from my SPH4B to pack out the ears some more and I have to say that this helmet combined with the CEP blocks out that much noise that I would say that a noisy stinky 8 hour day now feels more like 3 or 4 hours - the huge reduction in fatigue that I am feeling should be cause for further investigation.
Have heard people complaining about the avionics of Gallet but others swear by them. Given that they are made by the French is enough reason for me to steer clear. The Alpha? Well another colleague wears one & it is incredibly light - he has pulled all the attachments offa it and made his own sun 'motorbike' style peak - where my 84 weighs near 2kg his weighs about 800gms! I would gamble that any Gallet or Alpha wearer who tried a HGU84 would be convinced of the superior comfort & you don't have to annoyingly readjust the harness once you have the lid on yer scone as you do with Alpha. Took me a month to get used to the weight but neck mucsles have adjusted now.
Sizing. I wld go XL and use packing if needed. The XL HGU84 is very trim & sleek - what i mean is that it is not a huge clunker that will bang into everything - the XL is definately not cavernous. I have a very average size head, bloody ugly but a big brain.