I tried Mr. Beer and the Beer Machine, and never was able to make a decent beer with their kits.
I'd suggest buying a quality kit from a homebrew store that has grains, hops, and fresh yeast and easy to follow directions, and make that type of kit. It makes a HUGE difference in the final flavor of the beer.
I think of Mr. Beer like Campbell's soup. Not terrible, but not good either. A better kit with a boil and hops and some grain is more like a homemade soup with fresher and richer flavor and just a better quality.
Many people are satisfied with Mr. Beer- I have a friend who likes it a lot. But for those who aren't, and want something more like a commercial beer, a quality kit makes the difference.
For a 5 gallon batch, a 5 gallon carboy is a bit too small though as the beer will get some foam on top (called krausen) that can overflow out the top of the carboy if the carboy is nearly full. I"d suggest getting an "ale pail" bucket for 5 gallon batches to avoid blow-offs.