There are plenty of unbranded SATA PCI cards with more ports going for less than half the price of the Sweex 2 Port SATA PCI card, that said I would always choose a Sweex product over a cheap unbranded component.
I've built my own PC's for the past 10 years and of all the Sweex components I used none have failed, and like this SATA card most of Sweex's components actually come with a 12 year warranty!, not the 3 year warranty as listed in the product details. Sweex also has a easy to use website which has an archive of drivers for all their products, old and new.
As for functionality, this card does exactly as described. Install it into a spare PCI slot and it'll add two internal SATA ports to your setup. After installation both XP and Vista downloaded the drivers via Windows update and if your offline the drivers are included in the package on a CD. The card also has its own onboard BIOS so you can boot your computer from any drive attached to the card.
I have mine connected to a Samsung SH-B123L 12x Blu-Ray drive and it works flawlessly.