the general consensus is that they are significantly lighter and more flexible than other brands. my one friend's hyperflex 5/4 weighs half as much as his xcel 5/4 and ive felt this myself. (it wasnt water weight because his xcel had not been used in months when he showed me)
i forgot to add that ive been told they are not as durable and will not last as long.
no matter what wetsuit you get, how you take care of it makes a big difference in how long it will last
i use a 4/3 and am fine in the winter. it has no zipper so that probably helps. i have a seperate rashguard/hood that i use. good gloves and warm booties. altho i dont surf alot in the winter, it gets me by when the conditions are right...head high, sunny, light offshores, long lines.
the only part that gets cold my exposed face when i duck dive.
charging in cold water is no fun for me. but respect to the guys that do it. ill stick to the DOH+ stuff in the tropics.