After about one month of daily use, I'm happy to report that the Medium Cafe Bag was probably the best choice for me.
Sometimes (not too often), it gets a little too heavy for my current condition, but it has also felt a little too small (not too often), so I think it was the right size for my usual needs.
Waist strap experience for 5' 3" petite torso lady:
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I can and do use the waist straps fairly regularly for my typical days. (They work when I'm doing many errands in a row without too much hopping in and out of a car.) Even though I'm short in the torso, the MCB does fit me with the waist straps buckled fairly tight around my waist to keep the weight close to my center of gravity. The bag nestles right up under my bosom, and I feel like I'm carrying a newborn in a baby carrier, but this very effectively distributes weight and eases my day-to-day activities when my hand pain makes it hard to balance a swinging bag on the fly or my shoulder pain makes the weight difficult to bear. It's important to note that wearing it this way looks pretty dorky. Fortunately, I wear a lot of loose jackets (including summer high UPF sun protection cardigans), and putting the drapey jacket OVER the dorky waist straps leaves me looking closer to normal.
While visiting my parents in a small town where we often drive just a few minutes to a store (no traffic) and hop in and out, I found it better to take off the waist straps and store them with my luggage. Unlike the crowded conditions of stores and scarcity of parking in the urban NE, in small town Pac NW, I can handle the full weight of the bag on my shoulder for quick store visits and the dangling waist straps become annoying. I would put them back on for a mall shopping excursion or day in the city, however. While traveling by air, I would wear the waist straps around the airport, but buckle them together on TOP of the bag before boarding the plane and trying to slide the bag under the seat. That helped prevent annoying tangles.
I don't think I like the rubber shoulder thingie. I don't think I've ever put it to my shoulder as I usually minimize the strap length which pushes it down to the top of the bag. It feels wrong to do it, but I guess I'll cut it off as I've heard others mention.
Interior organization:
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I think I've read other threads where people wish there was a zipper on the main compartment (me too) or a tiny exterior zip pocket (me too.) I think some of this is "lady's purse" vs. "travel bag" preferences, and it doesn't make me DISLIKE the bag, but I've had to adjust my habits to suit the bag. I stopped carrying my fat leather wallet, and now have several thin wallets subdivided into special purposes. ID/major credit card/"specific travel card needed that day" in a tethered flat case; leather business card flap-over mini wallet for gift cards and membership cards; and a third slip-in style card case for my cards that relate only to being in my home state (in the PacNW) vs the state where I live now (New England.) I simply must have the currency and cards in the zipped pocket to feel secure. This is especially true because I can't always work the large buckle when my hands are sore.
Biggest trouble with this? I don't have anywhere better to put my lip balm than the same front zip pocket. It is small and will fall out of the open back pocket. It is small and will be annoyingly hard to find in the big interior pocket. Opening the flap and then pulling a tether and then unzipping an interior organizer pouch is WAAAAAY too many steps to grab the lip balm I use many times per day. I'm settling for going into the "money" pocket, but it makes me fear I'll accidentally yank out an important wallet/case and lose it while I'm distractedly applying lip balm on the run. I would LOVE to have a tiny pocket on the front of the flap for lip balm and/or a couple of tissues. I might try hanging some little pouch on the top grab handle, but I hate to make the bag less streamlined. There are a few--very small--items that I want to access immediately. That's never going to change.
I've found the rest of my things easy to organize inside the bag using a Q-kit, a mini Q-kit, and some other key straps and pouches (probably Eagle Creek) that I already had. I would like the bag better if there were an interior slip pocket to keep my iPad mini separate from the other contents of the big pocket, but that hardly rates as a complaint when compared to my lip balm issue.
Size note (regarding airline travel):
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It also fits perfectly in the ridiculously small Alaska Airlines first class aisle seat under-seat area where the electronics box under the seat divides a useful storage area into two less useful ones. My Aeronaut (45) wouldn't have fit there, but the MCB with Western Flyer both could. The person at the window in First Class wouldn't have this problem as there's no obstruction under that seat.
I hope my thoughts and experiences can be helpful to some other potential Cafe Bag owner. It really is a handy bag, and I love it in Dyneema. I really need a green one, though. Black is my least favorite color to wear!
--willo