Hi Viva,
I actually have the OG, not OMG. I have had it several years so had to verify with measurements. Sorry if my earlier comment was misleading.
I based my decision on the product photos. Looking at the model holding the OMG, I felt the larger bag would overwhelm my frame. I’m 5’4” with smallish frame. I was nervous that the OG would be too smal but that has not at all been the case. Everything I need fits nicely. The OG will fit under the airplane seat along with a small handbag along side (small Fossil satchel with crossbody strap this last week was just fine).
Angie’s comment about bulk is interesting. I have not found that to be the case for myself. I think the rounded top helps. The bag feels soft, stream lined and nestles nicely under my arm when I’m carrying on my shoulder. Perhaps that is the difference between the OG and OMG? The OMG is has bigger dimensions so maybe that is where the bulk comes from?
Looking forward to your assessment. I hope one of these work for you.