I only have one specific alloy housing, which is from ExtremeRC - or I guess I also have a Lander, but that is a complete unit that the housing can be used for a CS10 rotor, with blade trimming.
The ExtremeRC one is awesome (maybe all are?), because it is very well made and finished. It is almost the same weight as the plastic housing - so little more that it is unimportant. It comes with a motor housing/cone.
BUT... one "issue".... it is not made to take outrunners!!
If you have the ability/tools, you can easily mod it so it can take an outrunner. And that "hacking" won't bother it if you do a good job of it.