Kei,
Price, Price, and Price ... they were supposed to be very afforadable (mid- $100 price range if I recall the chat at Comdex 2 years ago).
Also they would utilize your AGP graphics card's output and the system bus, rather than have external or internal cabling from your card to the HDTV card and then out to your monitor.
I have a Radeon card with digital DVI out to my flat panel, thus I need a tuner that will output via my primary graphics card.
Bob