Frame bags are a great bit of kit but tend to have a hard life on a bikepacking bike. There is a strong temptation to overstuff the bag and this can cause the zipper to fail. Ortlieb has replaced the relatively fragile zipper with a roll top closure that's very close to fool proof and much less likely to fail.
A roll top closure is a great idea for a bag that's going to get used and abused out in the wilderness. The roll top is also an inherently more waterproof design.
The bag comes in three options, two traditional triangle frame bags that occupy the whole frame and one smaller one that fits along the underside of the top tube potentially leaving room for bottles (depends on frame size)
Size 4L = 24cm high, 40cm long , 6cm wide, 200grams.
Size 6l = 29cm high, 50cm long, 6cm wide, 250grams.
Toptube 4L =13cm high, 50cm long, 6cm wide, 200grams.