Just my 2 cents : I have this adapter in one of my PS2s, but i've been using it for its IDE connector :
With a certain boot cd (HDloader, I think), you are presented with a friendly GUI that let you choose which HD installed game you want to launch.
To put games on the disk, you can either connect the HD to a pc or perform a network transfer.
The game themselves are your typical ISOs from backed-up games (...).
Very convenient to have all your games ready to launch without ever having to get up from the couch !
Besides, loading times are usually faster than loading from disc.
Highly recommanded for PS2 gamers !