This is how my 50 DR renders its out of focus areas. I love it for portraiture, it's almost like having two lenses in one, except it doesn't lose sharpness wide open, just has a different character.

That said, if you can get a Leica, and you want one, and you have the cash, it will never hurt to buy one and sell it a month or two down the line...I would suggest that you don't bother doing any "testing" though, and just shoot. Whatever you get, provided it's in good condition, ought to work no questions asked.