Speed: ★★☆☆☆. Significantly below expectations for 8 bit gray in 600 dpi (a $200 Lexmark All-In-One WiFi printer is 2x-3x faster at scanning, and I'd expect a $50 scanner-only piece with no WiFi to be on par with it), and is just an absolute snail on higher resolutions (many times slower, even if you compute time per MB of output file). Think of scanning a full page at an extra high resolution as an overnight project. Also slow at previews and at low resolution scans.
Drivers & scanning dialog: ★★★★★. Convenient and has many options for advanced users. Doesn't install any services, tray apps or other crap. The only little minus is that the installer treats your desktop as a garbage can and spits out two icons on it (-1 to karma of the developer who wrote it and the PM who designed it).
Overall, I'd say ★★★☆☆. Well, speed is important and it sucks at it.