Looking on EBay for a longer stem for my CX bike, I noticed that there are a lot of cheap CF ones that cost less then some AL ones. Couple of questions here:

1) do you get what you pay for? Cheap = cheap quality = broken after a few rides?
2) is CF superior over AL?
3) what are these CF/AL combination stems? Clamps are AL and stem is CF? Are these joints compatable and strong?
example:


4) should I worry about 10s of grams weight wise?
5) would you purchase one of these cheapies?

TIA...