No break in on either brush; both of them are brand new. The 730HD shipped in the new Semogue brush box instead of the previous round plastic tube the brushes shipped in. As a result the 730HD knot is much more compacted not having the breathing room the 730 had.
The difference as noted is indeed the steeper shoulder angle. I've always liked the older style handle, but I can see this new style growing on me. Trying different hand grips the only grip that has a discernable difference of feel is when gripping the top near the knot with the fingers. You can feel the slanting down now of the 730HD vs the 730. There is just an oh so slight difference in the height.
The 730 measures 45.7mm tall with a smaller metal ring.
The 730HD measures 47.2mm tall with a larger metal ring.
There's been some changes over the years. I didn't even spot the change on the 620 and 610 until after rounding up the clear handled Semogues, and even with the older 680 model.
Left to right: Semogue 620, Semogue 610 red, Semogue 820 red, Semogue 730HD, Semogue LE 12 (Note slightly girthier), Semogue 730, Semogue Custom Boar '10, Semogue 680
Only the 620, LE 12, and Custom Boar have been used currently.