Not sure if this was intended, but I think this quite buggy. There is no output printed when the meta value is 0. I prefer to see it printed as 0 instead of empty column. There is a case I stored integer/number for the meta value.
So the buggy part is, the conditional check in file mb-admin-columns/inc/class-mb-admin-columns-post.php:54 make me no more possible to hook and customize the output that printed by the rwmb_the_value in mb-admin-columns/inc/class-mb-admin-columns-post.php:70 when the meta value is 0