It's pretty nice. It effectively gives you a "modchip" on a memorycard. You can use it on any ps2 as well. The disadvantage is that you have to patch them for the exploit (to be specific, i am using ESR for booting things, which you install after Free MCboot), but the discs still seem to work with swap magic afterwards so I'd imagine they would work with a chip as well. The MAJOR disadvantage is that it will only boot DVDs. You can convert CD games to DVD, but sometimes that requires somewhat more tinkering to get working properly. I've not tried it with dual layer games.

Once you get it set up though, it's very simple to use. Put your game and memcard in, start the system. It will come to a file manager for the stuff on the memorycard. You then run your ESR elf and your game will boot. It will even let you set different ELF files to the face buttons, so for example I only have to hit square to load up a game, instead of finding the ELF in it's folder and running it.