Im 5’7, and I reckon buy both the M/L and jumbo. Since jumbo bags are not on trend now, you probably will find a good deal.I hear you on this! I think the preference in sizing of the flap bags depends on your height/build. The M/L always felt small on me and I'm not a giant of any sort, but I'm 5'6" and a medium build, so that's why I lean towards jumbo - plus I plan to use it every day.
The M/L is on the smaller side for me, it’s not a day bag for me as I can’t fit my sunnies, but it’s a good staple and I generally use it at night. I find the double flap really annoying for daytime (like grocery shopping), so it’s probably the least used bag in my collection.