Anathema, I owned a Siren in the 1970's and can say that they are a great beginner's boat. I should, however, correct one of your misconceptions: she is not a keel boat, but rather a centerboarder (and although the manufacturer, Vandestadt and McGruer, claimed that the cast iron board, if bolted in the down position, made her self-righting - at only 140 pounds I wouldn't want to test it).
They were well built, easy to rig and sail, had reasonable performance,a large and comfortable
cockpit and four berths - although the quarter berths lack adequate
headroom for an adult to even lay sideways. Indeed, the
cabin itself lacks proper sitting
headroom and the amenities are better suited for daysails: for example, the
icebox provides space for a bag of cubes and about 6
beer, and the
head is really only a molded in bucket with a hose attached to the
deck for a pumpout.
The price seems reasonable and, so long as your expectations are not too high, she will be a great daysailor/occasional overnighter for you and your
family. I would also commmend the Sandpiper 565, mentioned by Sailorman, as another option: designed in
England, she has proper sitting headroom and slightly better performance.
Finally another couple of options to consider in Canadian-built boats, for only a little more
money, would be the CS 22 and Tanzer 22. Equally well built, but with much more space and performance.
Brad