I’ve been making framebags for about 3 years now and my conclusion is that zippers suck. They suck to install and then they bust. In just one week, I busted the zippers on my framebag, my top-tube bag, and a jacket. I threw them all in my gear closet and stomped away.
Then I stomped back to the gear closet, took out my sewing machine, plus a seam ripper, and got to work. It was surprisingly easy to retrofit a roll-top onto my previously zippered framebag. I ripped out the zipper and opened a couple side seams to lay the bag flat. I dove back into the gear closet to harvest buckles and webbing off a Camelback and fanny pack, both of which by the way had busted zippers. All told, it took about 5 hours of seam-ripping, sewing, scrounging, swearing, and finally satisfaction. The bag works great.