I have a Hammock Gear quilt and they came in either sewn in footboard or snapped. I tend to get cold feet so I ordered the sewn box so I assumed it would be less likely to get a draft. A snapped box could also serve as a blanket it is unsnapped which didn't matter as much to me. Their unsnapped would be tapered.
Most things are obvious but some arent. Non tapered is heavier, easier to make, more room in the foot box for feet and pad. Downside to more space is that its more dead air to keep warm. Upside is that if you decide you want a non tapered pad it will probably still fit inside the foot box if you want. Tapered is lighter, possibly cheaper to make if using down, less room. Could be warmer on your feet if it minimizes extra space around them. Youll probably need to always use a tapered pad if you want it inside the quilt. I have an EE and a little less taper wouldnt hurt my feelings at all.