I accidentally purchased one of these (5513) must be the BP case although that’s not how it was advertised.
Me too, I don't really know what it is for sure, but I'll add my two cents on my 'JKF' case from 4 or 5 years ago...
The case is well made and the case neck is oem spec.
Case threads will accept oem spec case tubes.
Case neck is oem spec and will accept oem spec crystals.
I used a DW 'spring wire' bezel assembly on mine with a GS crystal because an oem spec bez insert was a good snap fit in the DW bezel (on this particular bezel).
All in all, the case is Ok for the $$.
One Major Gripe...
The lug holes are bored too high in the lugs and when drilled out to 1.25 or 1.3mm they are too close to the tops of the lugs. For this reason I put it in File 13.
Btw, the lug holes were drilled out on a milling machine, not a hand drill or wobbly drill press so they followed the original holes and did not 'go sideways'.
Looking waaay back...the best cheapo 5512/13, 1680 cases I have are the old 'ABAY' cases from 'Paul' in 2005 or so. They are oem spec (case neck, case tube threads in the case etc.) but they have a bezel setup worse than most spring wire bezels...the crystals are glued to the the case neck.
Besides that, the crystals have a 'mushroom top' that holds a non oem spec spring wire rotating bezel on the crystal and it all falls on the floor sooner or later.
How it works: The spring wire holds the bezel assembly to the crystal because the 'mushroom top' of the crystal is a larger OD than the crystal sidewall. You can pop the rotating bezel off with a fingernail. Usually, they just fall off.
One smaller imperfection is the case back gasket groove is machined in the case, not the case back like oem but this does not matter...to me anyway.
One other problem is they were all made to use 26.5mm dials, a 5512/13 26.0mm dial is not a good fit.
One upscale goodie is the ABAY COMEX models have oem spec escape valves, I compared them to a nos oem example.
Another upscale goody is they came with new Swiss ETA 2836-2 movements, no referb junk or clones.
New/nos Swiss ETA 2836-2 could be found back then in large quantities for $50 USD or less and I still have a few from back then that were $65 or less from USA supply houses, purchased one at a time. Swiss ETA 2824-2 were the same price or maybe a little bit higher.
The best way to find new/nos Swiss ETA 2824/2836 'bargains' today is to buy a forgotten brand or discontinued nos watch with one in it.
Example: I found some nos 'Gruen Swiss' models with Swiss ETA 2824-2 still in their boxes that came from Walmart closeouts for $40 each.
Walmart took a run at selling higher quality automatics 15+ years ago and they flopped...their customers wanted cheapo quartz watches.
Here is a Walmart Gruen for sale on eBay:
item number: 315555037195