I have several different USB tuners now, and each and every one is different. Things to consider:
1). Will it work with Window 7 Media Center? If no, you might want to pass. If yes, then on Windows 7, this just plugs in and works. This says it supports Windows 7, so that is good.
2). Does it do "Clear QAM"? Over the air ATSC is HDTV broadcast, and with that, it will receive BROADCAST HDTV from an antenna, IF there are signals in your area. It requires a good antenna usually if not close to a big city. Since Analog (NTSC) broadcast TV is mostly gone now, that is mostly useless for over the air.
However, QAM is the transmission method for digital cable, and an ATSC tuner will NOT tune digital channels on cable. A "Clear QAM" tuner will be needed, as all digital cable companies are required to send standard channels (the ones they get from local broadcast) in Clear QAM, unencrypted.
This device DOES NOT do clear QAM, so it will NOT receive "free" digital cable channels.
3) NTSC tuners for cable: Some cable companies still send 32 or so channels in analog NTSC over the cable. But it needs to be a "cable" NTSC tuner, and not just an over the air tuner, as the frequencies are different. I suspect this is not an issue. These are NOT HD channels!
Conclusion: If you do not have cable, or your cable still transmits some channels in NTSC. and you can receive over the air broadcast ATSC, then there is some use for this. If you get your TV from digital cable, then this is likely not going to work.
As for working on a Mac, I would not count on it, as I could find no driver for the Sabrent tuner chip for the Mac, nor could I find one for Linux either.