I had a few customers that used Barley, all but one had a Losch boiler. Those could burn anything from barley to pea. One customer used it in a EFM.
AFAIK besides the price there is no benefit, I do know one thing. You probably do not want to use barley during the summer. We had a stretch few years back where it was hovering around 100 degrees for 5 or 6 days and every one of those people burning barley called to complain there was something wrong with the coal and they couldn't keep it lit.