I've played competitive Magic so I've had my hands on more sleeves than I care to count.
Ultra Pro's are perfect for Magic because they're consistently sized (usually! I have had issues with this before) more importantly they're tough and durable.
Actually, my favorite sleeves for Magic are Dragon Shields because their durability surpasses Ultra Pro by far.
But this is a question about FFG sleeves.
From the sleeves I've seen so far (I just bought Return of the Jedi movie poster art for the purposes of sleeving my X-Wing minis cards, and I've seen the cool lightsaber art sleeves) my initial reaction was "Wow are these things thin and light."
I don't think they're very durable, so in an 8 round Magic tournament that involves any amount of tutoring or fetching, I think you may start to see problems really quick.
But, I also bought the small clear sleeves (the yellow one, I forget the size name) again for the purposes of sleeving my X-Wing minis, and those are some nice sleeves!
Anyway, there's my $0.02