Would that work?
Likely not compatible, Just buy the My Passport SSD or the NEW My Passport Wireless SSD. Check 'em out!
I already have the TB Duo, the goal is to gain speed - if possible.
The Thunderbolt connection will be the Speed Bottleneck … and i doubt you’ll see any significant speed gains for the higher price / smaller capacity of SSDs.
SSD’s are significantly faster for launching applications and boot times … data transfer, not as much, due to speed bottlenecks of data transfer connections.
Hold on, wouldn’t Thunderbolt’s 10 Gbit/s be enough?
It should translate to 1250 MB/sec, wouldn’t it?
things that should translate, most often don’t
the only way you will find out for sure if want you want to do, will work … is to do it.
lets us know, how you go 
I have 2 MyBook TB Duos daisy-chained and interestingly I could gain speed by placing 2 SSDs in separate boxes in Raid0 - see screenshot below. Not stellar speed but good enough for my needs and not that expensive.
When they were in the same box, the speed was about half of the below.
The other 2 drives in the boxes are WD Reds and used for backups.
The actual bottleneck here is the internal SATA interface to the individual SSD. Your read speed is the maximum that can be transported via SATA3 (6 Gb/s = 750 MB/s).
