Ok I took some comparison photos of the handles of the shoulder B29, B30, and B25. Of course the B29 has the longest handle and I never realized how tiny the B25 handles are lol. The B29 is also more compact compared to the B30, not just the height but also the depth, and it seems to be the middle ground between the B30 and B25. I think it would be great for someone who wants something a little lighter and less bulky than the B30, but wants a more comfortable handle than a B25. (Of course the aesthetics of an east/west bag are also different from a square bag.) I love my B25’s and I use them a lot, but the handle is definitely very small and I usually hand carry and have to be careful if I slip it onto my forearm. The B30 seems cavernous compared to the B25 and B29 and as someone who doesn’t carry a lot, it is my least used size.
I also measured the opening of the handle from the back, because the opening is actually smaller from the back vs the front. This is not the total handle drop length, just the opening where you would slip your hand/arm through, and of course there will be some variability given the hand made nature of the Birkins.
Handle opening as measured from back of the bag
B25 : 6.5 cm
B30 : 10.5 cm
B29 : 12.5 cm
View attachment 6206955
I propped up the B29 so the top of the flap is about the same height as the B30 and B25 to make it easier to visualize the difference in handle lengths.
View attachment 6206956
View attachment 6206957
Side view- you can see the depth of the B29 is similar to the B25 and both are smaller than B30
View attachment 6206958
From the back to illustrate the size of the handle opening.
View attachment 6206959
Hope this helps!