I would use it both of mine where pre term babies and i choose to formula feed in the end.
With Kimberley i was so sick and i couldn't get myself to b/f and with Alex i tried to express but i didn't have the right support to carry on and i had to hand express which really hurt me.
So if this time round i have another premmie baby i will use it if i don't get the right help and support to get get my own milk going.