Housing fit great and looks great. Internally mine was cleaned up really good. I used a better gasket then what came with it. Everything else lined up fine. Overall for the price I dont think it can be beat.
I am happy with my Megan O2 Housing. I also have the Megan resonated test pipe, and I am very happy with the overall build quality with both pieces. The welds are very good, and all the passages are ground smooth on the inside of the O2 housing.
Overall, a great piece for the money, you really can't go wrong.
I can't say for sure as to power gains, as it is not yet installed on my car. An aftermarket O2 housing is absolutely necessary for freeing up the back pressure just behind the turbo, and most if not all of the pieces on the market will work just fine as long as they have been properly engineered. I decided to spend a bit more money and buy the Megan over the eBay special, and I'm happy I did. It is just a nice, simple, affordable, well made piece.
It was very easy to install and it came with all the necessary hardware. You do notice better performance from your engine.