Now that I've gotten this lid home and had a good look. It's is seriously chunky. Like to the point where the half lid looks stupid lol.
It has a different (new?) Mips system in it called spherical mips, which seems to be where a huge chunk of the extra bulk comes from. It's two layers of eps in a ball and socket configuration (basically a helmet inside a helmet lol), plus the liners plus the floating adjustable cage the liners go on. It's easily a third chunkier around the head.
Chin guard is shorter (closer to the mouth). The chin guard is stiffer and the foam is reinforced with what looks layers of some composite/resin sheeting. Definately stiffer and thicker.
Hearing is somewhat diminished as the chinguard does away with a couple holes where the ears are between the two models.
One thing that I don't like is that the metal latches are now some sort of hybrid. There metal parts for hooks, but the latches are plastic. Kind of takes away some of that confidence. The rear latch mechanism which holds it all in place looks like it could be subject to wear more so than the 3r. Something to keep an eye on and double check before riding.