2*mSATA/NGFF >>2.5"SATA2/3 adapter?

I need one. RAID, plain (seen as two drives, expander/not... just something that will combine two mSATA/NGFF SSDs into a 2.5" disk space, that I can use in a laptop.

Has anyone foiund something working for the above scenario? TIA
I've seen some different adapters, but for each there are gotchas (some only see one drive, and let you choose which one, with a pin setting, some require expander support on the controller part, some combine them, but output a 2.5" "double SATA" drive, which makes no sense, etc.).
Storage is the primary concern, but speeds must not be made noticeably worse than what a single SATA2 SSD would do.