Banana skins my be some of most heavily pesticide/fungicide treated of any fruit there is - I'd get the organic ones if you plan to do this with the skin. I think the bitterness come from the white stringy/pithy stuff between the banana and the skin.
One way I was able to use banana without an overwhelming mess was to put in in a nylon stocking. That is a finer mesh than most grain bags and kept the sludge from distributing through out the mead, though a lot of fluid was lost when removing the bananas. That's very similar to the problem with mangos, and I'd like to try the centrifuge idea on it the next time I do a batch with a bunch of bananas.
I think seriously over-ripe bananas work best.
Lanne pase toujou pi bon
(Past years are always better)