So, I ordered a few of these to play with, 2 of the 4 had physical damage and can't be racked, waiting on the vendor for replacement. Shipping box and packaging was fine, so I assume they were damaged when removed and not noticed when they packed them up for shipment.
They came with both mezz slots filled, one with a 2x 10gb sfp and one with a 3008 LSI mezz card. I replaced the LSI mezz with a 3108 series mezz, easy swap.
I was concerned if these would be serviceable (replace a HDD) without shutting them down, and to my surprise, they are! You can pull the front of the system out that has the HDD's in them while the unit is running, which allows you to service/swap HDD's, without taking the unit down or out of service...risky but doable.
The 12x 3.5" are SAS only, the 4x front 2.5" are SATA or SAS, and the rear 2x 2.5" are SATA only. The 3008/3108 LSI raid supports the 12x 3.5" HDD's and the front 4x 2.5" SSD's. The rear 2.5" are NOT supported by the LSI raid mezz. There is a PCH bios setting for these rear slots. Not sure if they are fake raid or what, but I haven't found anywhere to setup raid on the rear 2x 2.5" SSD's yet.
Some pics and a short video showing the system and the ability to "slide out" the 12x 3.5" portion of the server -
https://photos.app.goo.gl/ftqiaSWYK3WzXctaA
It looks like these were part of some large CEPH or other distributed storage setup at some large cloud provider, they have labels on them with various StorageX notations, storage127, storage4, etc.