if you save BL to a flash drive, it'll ask for the key each time you change computers
the key.dat file is written with the computer, based on the computer, so you can't switch computers and have it work, which helps prevent key theft
so either have 2 different files, one for one computer and one for the other, or have 2 key.dat files which you switch out/in depending on the computer
or do what you're doing now :D