It's a good deal and a good lens and camera.
The Biometar is *identical* to the early f/2.8 Planars, like the ones used in Rolleiflexes etc.
It's a quite better design than the f/3.5 Tessars and their clones used in almost every other TLR (Yashica, Meopta, slower Rolleiflexes, Minoltas, etc.).
Faster, sharper and contrastier wide open, with less field curvature and astigmatism.
Think of it like that: with $100 you could buy a good 35mm SLR, or you can go medium format with a really good lens (and also access to other amazing, and cheap, lenses like the180mm f/2.8 Sonnar).
My opinion is, go for it.