$180 is a good price for the 2-tuner model. The AirTV BB is (regularly) $120 (don't know if AirTV will have a BF sale) but you have to add your own HDD, so it comes out about the same.
$220 for the 4-tuner model is even better. As for the need, I guess it depends on your TV viewing patterns.
For me, two tuners is enough 95% of the time, and three would cover at least 99%, maybe 100%. But if you're a heavier TV viewer and all the shows you like happen to be on at the same time, you might really need four tuners.