I recently scored a Bridgestone xo-1 in my size, with the stock m-bars. This bike came with dummy brake levers mounted backwards, around where the tops would be on drop bars, to simulate this hand position. I had previously ridden a friend's bike with m-bars and didn't really like them, but the dummy levers seem to make a huge difference. I even found a hand position where my palms are on the dummy levers, my fingers are on the beginning of the swept-forward portion of the bars, and it feels like resting my hands on a table.
I've never toured with these bars, and I've only been riding them for a couple of weeks, so I may grow to dislike them eventually. However, for anyone considering m-bars who isn't too concerned with the goofy appearence, I would recommend trying them with the dummy levers before forming a firm opinion.
-GG