I (and I am sure others) have implemented RAID on top of multiple USB sticks on a USB hub. But the documents online which describe how to do this all seem to say "don't do this" For the same reason: when it breaks, its horrid. unlike devices designed to be ganged up, removables have pretty bad failure modes. I would hope the micro-SD has better ones, but I am unsure.
The device looks like its maybe designed for fast parallel programming/writing to cards.
Surely seek times on this are atrocious though? (Even considering that the reads/writes are being striped).
That they're both flash storage does not mean they're interchangeable at like capacities, and I'd expect this to be slow and prone to constant errors. I don't think it's a fun if impractical hack, though.
The device looks like its maybe designed for fast parallel programming/writing to cards.