(1) Very comfortable, virtually indistructible, very little restriction of movement, pockets in the right places and a buttoned baffle across the front for drafty cockpits. The side pockets zip reducing FOD risk. There is a concealed waterproof hood. They are also very warm whilst being quite thin - they are happy with a LSJ over the top (whilst my other flying jacket, a USAF B-3 copy is very uncomfortable with anything over the top and much more restrictive in a cramped cockpit - although much nicer in a totally open cockpit). Oh yes, it takes badges well too.
(2)
http://www.airstoreone.co.uk/proddetail.asp?prod=ic3e; 57*153*35 mm (plus knobs and a rubber duck antenna stuck out of the top), 465 grammes.
(3) Just next to (and outside) the main zip slightly to the right of my left nipple. (And before anybody asks, that's in the same place as most other men's left nipples).
(4) Nope, and you can ignore them if it's not drafty. Big, chunky, only four, and easily handled with gloved hands.
(5) Not in my experience, I've flown fast jets, microlights and the odd helicopter - all wearing a helmet, whilst wearing one of these jackets and never had any discomfort so long as the collar is properly tucked down.
(6) For British winter yes, I can't speak for anybody else's winter since I only usually fly in ours.
In fact it may be the only bit of British military flying clothing that is better than anybody else's (except maybe the cape leather gloves, and those are too cold in a drafty cockpit).
G