After reading the TSB the only detrimental effect "possible"created by changing oil thru the drain plug was a chance of getting drain oil on rubber suspension parts. Maybe because of the location of the engine in "some" Mercedes products that could be a problem. But going by the location of the Drain plug on the Crossfire, you would have to be pretty sloppy to get oil on anything but the bottom of the pan.
Also the TSB clearly states that pumps that use a tube that slides down to the crankcase through the dipstick tube shouldn't be used. Most of the extractor pumps I've seen work that way.
Personally, I think the main reason the dealers use the extractor is because it's easier and saves time, and as we all know, time is money.
My car sits flat on the ground when I change the oil.
I put 8 qts. in and I get 8 qts. out. My dipstick reads full at 8 qts. and I've never had an overfill, or low level light come on.
Just go with what ever you're comfortable with.