I'd be very interested in a comparison too. I've been a huge Final fan for years now, with the Heaven V being the first pair of headphones or IEMs that really wowed me. Eventually upgraded to the Heaven VII as my daily driver, which I absolutely loved, until they stopped working about 6 months ago. Just got the Meze Rai Penta (which ironically also translates to Heaven V) in yesterday and I think I found my endgame IEM as I've been struggling to find anything I dislike about them, from the sound, to the build quality, to the comfort. But then I'm just finding out today about the B series and was surprised that Final is trying out a hybrid design with the B1 like the one that the Rai Penta has since they've always been single driver purists for the most part. The B3 is also really interesting as it seems to have a similar sound signature to the Heaven VII based off the impressions I've seen. I don't think I'd get anything from this new B-series line since I'm so happy with the Rai Penta, but I'm going to keep following the news about them since it seems like Final is going through an interesting transition phase with this new line. Maybe when their new vision fully matures, I'd be interested in getting a new flagship IEM of theirs.
Btw, I'd be happy to do comparisons with the Rai Penta for anyone who wants to send me some loaner pairs of the B-series haha