I have a Bav 30 with the tandem keel. I wouldn't necessarily have chosen it (boat was 2nd hand) and on the West Coast of Scotland it's rare to worry about depth. I haven't sailed a fin keel version, either normal or shallow draft, so I don't have anything to compare directly with, but I certainly don't have any complaints about performance. I wouldn't let it put you off if the boat is otherwise in good condition. My hull has been coppercoated, but there's a few rust spots breaking through on the keel itself, plus the bottom of the bulb was not coppercoated so has got quite a bit of surface rust. it's definitely worth getting the surveyor to give an opinion on the state of the keel. Opinions vary on getting it sandblasted and re-epoxied, or just wire brushing and sticking more anti-foul on and forgetting about it. I would suggest condition is as much a consideration as fin vs tandem. Oh, you need to get used to the lads on the hoist asking if you know you have a hole in your keel (every year).