Read Amal’s response in this thread.
While it’s flexible, its not meant to put in areas that will be flexing all the time. There is a lot of movement in that area which may not the best place for it.
Other hand locations I’ve seen are top of the proximal phalanges (if your finger is big enough), the back of the hand, and the “knife edge” (karate chop) area of the hand.
Installation of the flex is more involved than the X series. There are a lot of nerves, tendons and blood vessels in these areas so make sure you go to a qualified installer.