Having played with the AirAsia unlimited ASEAN pass back in the day... I can almost guarantee this will cause more frustration than it's worth. The biggest caveat is that there is no obligation for Frontier to release seats to this pass; and at this point, we have no way to know/check what seats will be available. A flight could be 50% full, and Frontier would be within their right not to release last minute seats - not saying that is the case, but without concrete terms such as "if xyz fare class is available, you can book these seats", it's just a giant gamble.