I flew one of these trans Atlantic with a friend many years ago. Nice plane, but compared to a C310, or similar twin Cessna, a little frustrating for fuel quantity. The 303 had a fuel quantity indicating system which seems no better than the single Cessnas. With only one tank per side, when the pointer starts bouncing between 1/4 and nothing, it's hard to judge how much is really there - a little un-nerving when you can't see the coast of Iceland yet (pre GPS).
The early C 303's were also REALLY nasty in icing, before the addition of the electric pad in the middle of the tail. Silly me did not read the flight manual before flying (too much 310 and 340 time - though I could just figure it out). The guy before me did not install the AD required placard prohibiting flight into known icing. The plane was all over the sky in pitch and yaw for about half an hour 'till I got lower and found warmer air. By the time I landed, it flew perfectly, but had no ice anymore (clue 1). It was actually a few legs later (bored between Iceland and Scotland) that I bothered to dig out the flight manual, and read about what almost happend to me and why!
Lessons learned: 1) I like planes with more tanks than engines, if you're willing to actually manage the fuel, it's a bit more reassuring later in the flight, 2) Read the flight manual!
Cheers