I think most folks under estimate the amount of engineering and thought that goes into sail bags, and how extremely difficult they can be to build and even more so to customize.
The north bags are by far the most useful out of all the brands I've used- ullman are certainly the worst, and Q don't have all the kinks worked out.
The bags are J-length (mast to headstay) for a reason, the break between the front and rear of the zipper are there for a reason, the way you can reach the clew from the back of the bag without breaking the zipper, again there for a reason.
Length- full length bags mean more weight firstly, and that might not mean much for your 35'er but higher in the range (say a SC 70) bag weight becomes a factor. So as most have pointed out, if you want full length bags, ask (they're probably extra). But the j-length is good because you're bow team is on the bow, and not in the way of trimmers,etc.. in the back while hooking the headsail up.
Zippers- it's called a fresh water rinse once in a while. I make a point to spray the shit out of the zippers with water after a regatta, and mclube them as well. The NS bags are designed to better control the sail while hooking it up- if properly luff stacked you can open the front zip, hook up the tack and head, and reach into the back of the bag and attach the sheets to the clew without breaking the zipper- then when you're sure that sail is the call, you can break the rear zipper and send it, all the while the sail was contained.
Now as far as handles- those tend to appear once the bags get longer. especially for bigger offshore headsails. they'll have handles and external ties for tri-folding (leech stacked jibs) for better stacking.
With the movement to furling kites and whatnot, those require a different type of bag.. usually custom, but well worth it.
Bottom line though, ask your salesman at the time of sale about what features you want on your bag.