Like mentioned above - they just work.
I have a backup that I have never needed to use. It did take a while to synch the unit with my other image bank.
My plan is to one day take a long 2week trip with nothing but the two imagebanks and shoot until the digital back is smoking

I dont mind the "kidney bag" as I am already using a tripod and the connector is excellent (has never pulled out)
Only thing I can mention is to be sure if you can use the old style units or Image Banks II. May not be an issue, but I recall
seeing that some backs need the newer styled units?