As far as the sizes go, the first one refers to height in centimetres, the second refers to chest in centimetres. I'm not too sure about 180/96 being small (I'm 5'7 and use 170/96) and the 180/120 being extra large (except in the chest).
I have one of these (though from a different seller) and I can thoroughly recommend it. An excellent windproof layer that goes over the top of everything else and has lots of pockets. When I'm doing fieldwork in the winter, this is my go-to shell when it's not raining and it's normally worn with either a heavy Herlly fleece or a primaloft jacket under. I've added wire to the hood to make it more useful.
Check my comment on similar thread today, they are ok, not brilliant but they do they job. Get a good needle and thread and cuffs for the wrist. Holds wind off well but not of genuine smock standard. Hope this helps. PS this is the supplier I bought off. Fair price and I wear it a lot.
As I needed something a tad larger in size than these things come in I went for the Jack Pyke version in woodland oak and it comes with a very handy waterproof flap at the back which can be used as a poachers pocket or unzipped completely and the flap drops down and is used as a very dry comfortable and warm padded sit mat. Waterproof and warm, soft to the touch and quiet. I can highly recommend them. Have a look before you choose. Alittle more expensive but a little more utility features so worth a glance.
not waterproof like the artkis, but windproof, plenty of pockets and easy enough to treat, also got some memeory foam knocking around here from my bike days, am going to chop it down for the elbow pad pockets... not because i need them for sniper purposes, but because im getting old and like a bit of softness where i can get it
really really want a ventile double layer smock, but cant afford/justify the £200-£300 to get one