BSAs have a bad reputation for being very inconsistent, a real crap shoot in getting a good one, some love them, some wouldn't touch one. On Rimfire Central, for use just on rimfires mind you, they have several derogatory descriptions for the letters B S A, so as Rusty said, be forewarned.
I've only used two, one on a spring airgun that was recommended by Lawdog here in the airgun forum that has held up great, and a red dot that fogged up inside on me the first time I used it in foul weather.
Tim