Are they hidden, or just poorly advertised? Why not both? Over the past few years I've added features to the Board (mostly by request) that might not be so easy to find unless you have a very keen eye. With apologies for that, here's a quick GIF demo of where to find, and how to use, the Big Board's hidden features.
As shown in the GIF demos below, each of these is found by selecting the header of the column of interest. A dropdown arrow appears, and clicking it will reveal a list of alternate things that can be displayed in that column.
BIGz - can be switched to any of 5x5z, Puntz, BIGAA, 5x5AA, or PuntAA
Rank - can also display any of these 6 valuation systems, which allows you to compare them
Pos. Rank - can be switched to calculate the difference (in dollars) between the values in the BIGz column (note in the GIF, it has been switched to 5x5z) and any of the other systems currently displayed on screen. It can also be switched to display each player's MLB team.
ESPN - can be switched to either Yahoo or CBS. ADP or AAV also update accordingly to that site.
ADP - lots of options! Average draft position (ADP) is default, but it can be switched to show either NFBC or FP (Fantasy Pros) ADP's, AAV (average auction value) for the selected site, or ESPNk, which is the ESPN keeper rankings.