Wow what a fantastic review and pictures. Thank you very much.
This is a beautiful watch and will likely be my second Royal Oak. I previously owned the TW version that had a closed back, with a Swiss ETA and gold-tone screws on the bezel. Not 1:1 construction style, but it wore nicely. I am planning on the white dial version 15400 from the new factory. My reasoning behind going with new factory vs the BP version is mostly based on the decoration of the movement but also thickness. The BP may have a gen swiss movement, but the finishing is too basic and not worthy of the rest of the watch. The canon pinion on these BP ETAs is better suited for Rolex clones with the tall clearances between the hands. I suspect that is where the extra 0.9mm in thickness comes from--after reading your post it is then coming out the back... is the rehaut the same depth? I wonder...
The new factory version has an 4.6mm ETA 2824 clone (25 or 26 jewels depending on the design) with a beautiful radial Colimaçonnée (diamond cut snailing circular finish on the perimeter of the bridges), and Côtes de Genève or "Geneva stripes" on the winding bridge. Additionally on the winding bridge perimeter step down there is snailing. The 2824 dates back a few decades and has been used in high-end watches with very nice decoration--similar to the way it is on the AP RO rep. It looks good and is a reliable movement from experience (assuming it is the same one that Noob is using on their V2 sub, IWC Vintage Ingenieur).
I am looking forward to see the upcoming 24 jewel 3.9mm Miyota 9015 version, which I was told by Angus should be out within 2 months (hopefully that is a well-padded date) , has the Geneva stripes and a plus is the winding rotor center bearing which sort-of resembles the 45 jewel (officially 40) 4.25mm thick AP 3120 part at least more closely than the single screw and copper colored bearing of the winding rotor on the ETA design. One small detail is that the main plate does not have decoration--only the automatic winding bridge does--at least in the 9015s I have seen on the Internet so far.
A down side (as far as replication) of both of these watches is the beat rate of 28000vph (4Hz) or 8 ticks per second, but it results in good accuracy in timekeeping and looks very smooth vs. the genuine's 21600vph (3Hz) or 6 ticks per second. If this is an issue the drive train from an ETA 2846-2 could be substituted assuming it fits the Asian clone counterpart. I would leave it alone at 28000vph.
Someone mentioned their curiosity as to why the slim 21 Jewel 3.6mm Asian 2892A2 clone--the rather excellent SeaGull ST18--was not used. Frankly I am very fond of that movement due to its performance. I purchased it on an Omega Speedmaster James Bond 50 years watch from the BP factory, and transplanted it into a blue SMP-c from the same BP factory, and I can say the movement is very accurate and well decorated.
The only issue with the ST18 is the same as would be using the ETA2892A2--the winding rotor mount is very peculiar looking and resembles the gen even less. That said, I like the movement so much that I would buy more watches with this movement.
My $0.02.
Beautiful watches btw.