BUILD Aint this some kinda fun!

[Stux]

Velcro, technology's duct tape.

Panduit Tak-Ty is great for bundling cables without all the thickness of velcro though.

I like using 3M command strips for mounting SSDs. They're rated for multi-kilo loads, and come off cleanly. Just remember to leave the tab exposed.

I used this to add a SATA3 SSD to a Mac Pro 2009 (pcie2/Sata 2 only, but dual x5680s ;)) before the m2 SSDs became a thing

If it'll boot a Mac Pro it's gotta be fairly standard. Wouldn't recommend it as a FreeNAS solution though. Would be better to just use an m2 ssd (ie SM950 Pro) mounted on a 4x add in card if you want to get an l2arc into a system with a free PCIe and no Sata ports. You can get 2.5GB/s reads from those.

Ps: haven't tested either with FreeNAS.