This pickup is supposed to have a vintage sound, and it does. It has an even sound across the strings, very little hiss, and seems very solid. You can probably mount and unmount it 100's of times without having it fall apart. And Seymour Duncan pickups actually have an after-market value, so you can sell / trade it for something else if you want to get something else.
I just wish it wasn't so bassy, but that is a problem with most Stratocaster neck pickups. Lately I've grown tired of that "Strat"-sound, so I'm going to be buying a Seymour Duncan Little 59 (neck), to compliment my bridge-59 which sounds just fantastic! My 59 has a very characteristic "twangy" sound that works for many different styles, but this SSL-1 really only shines for blues IMO.
On Seymour Duncans website, they have small demos, so you can hear the differences between pickups. I suggest everyone spends a little time there before buying. Last piece of advise: Don't buy cream-coloured pickups! They look horrendous after a couple of years =).