When is a duffel the right choice ? We prefer this HUGE roomy backpack of OZUKO #9309 !

I’m planning a two-month trip around the world, mostly focusing on Southeast Asia. Since I’ll be traveling for a long time, I’m looking for a bag that gives me enough space for my clothes, laundry, and potentially some extra for souvenirs I might pick up along the way.

Right now, I have a Tomtoc 40L backpack, (which is closer to 35 liters imho), and I feel a bit limited by its size. I’m considering getting something slightly bigger, and the Osprey Fairpoint 40 is a popular recommendation. However, I already own a 50L North Face duffel bag (S, 50L), which I used during an Interrail trip in Europe.

EDIT: Since I’m seeing many comment about this: To clarify the TNF Duffel bag has backpack straps! I do not carry it with a single strap across my chest.

I found the duffel bag to be OK for limited Interrail trip, even though many on this subreddit mention that duffels are more uncomfortable compared to proper backpacks. I’m wondering if there’s any reason I shouldn’t use the duffel for my upcoming trip?

I’m planning on using packing cubes to manage item placement. Is there anything else I’m forgetting to consider before making my decision?

The excuse to get a new bag is always tempting, but if I can save myself from buying something new by using what I already have, that would be ideal. Plus, the duffel has compression straps, so I could underfill it and still fit it into overhead compartments on Asian airlines (or is that still a compliance risk?)

When is a duffel the right choice ? We prefer this HUGE roomy backpack of OZUKO #9309 !