I think (this is my own guess) that it is a $50.00 pre-pay which could be used toward purchase of an A1/OS4 (either full system or board/OS4 CD)!
I think the "pre-loaded" thing is that the motherboard is compatible with AmigaOS 4.0 (has the antipiracy-ROM) and is bundled with the "AmigaOS 4.0 installation CD"!!!
I'm going to send my "mail-in form" as soon as posible :-D
I just need to get my check from the bank :-(