The S2A was also my first medium format camera. I think $50 is a ridiculously low price; I believe most kits catch about $200-$300 on ebay, depending on their condition. Since your friend is selling it to you, I'd imagine everything would be working fine with it.
What's nice about the S2A is you can get some really good lenses for pretty low prices, at least compared to Hasselblad lenses. Both of the Nikkor 50mm lenses were great, I don't believe I was ever impressed by the 135mm, but the 200 (or is it 210?... it's been a long time...) performed very well. Personally I never tried the Zenzanon or Komura optics, the only reason I bought an S2A was because I wanted the Nikkor lenses.
I was a bit sad to see my S2A go... I sold my entire kit, with a 50mm F2.8, 200mm, a couple extra backs, prism, grips, etc, for about $800 and that only paid for about half of the Hasselblad I bough (with only one lens!). I can honestly say I questioned that move a lot, but I do have to admit the Hasselblad was a bit lighter and as weird as it might sound, I really liked having the shutter-speed dial on the lens; it just felt better for me.
I've since moved up to 4x5 and sold my Hasselblad and am trying to decide when I get enough money if I want to buy another Hasselblad or buy an S2A instead... it's a tough choice... I really liked them both...
Honestly, the only medium format brands I personally would consider are the Bronica S2A line, and Hasselblad, I didn't like any others.
Of course, at that price, assuming everyone works fine, I wouldn't even hesitate a moment to buy that S2A... That's such a good price. If I knew your friend I'd buy it off him in a second!