Agreed that a direct connection with an usb cable is cheaper and more reliable, but then the whole point is about controlling multiple H9s. Unless you want to use 4 USB ports AND loose the midi ports functionality on all the the H9s it is better way to rely on Bluetooth at a SHORT distance. I never tried with four H9s, but bluetooth works very well for me with two H9s.
Also think that you will probably need the midi ports on the H9 someday if you want to set them all to the same tempo, or have them "talk" together for any other porpose.
LA
