Did you mean this one?
http://www.racemmi.com/
The website is a bit sketchy, not going to lie. Personally, I wouldn't feel comfortable ordering that expensive of a kit from either of those locations. This is the kind of work where you want to make sure you get quality parts. I can't open the ebay link while at work, but on the site they don't even mention what model or brand of turbo they are using.
Also, while this kit might be turn key from the hardware side, the tuning will still need to be done. On top of this, if you're looking at twin turbos there are a LOT of engine upgrades needed to handle that amount of power. With the amount of boost pressure that you can get out of two turbos, you would need much larger fuel injectors, probably a fuel pump upgrade, and would likely have to build the lower end. Another concern is their mention of working with the factory exhaust. It might be doable, but I would imagine you would need to update the factory 4.8 exhaust to handle the flow that system would put out.
All in all, I would avoid this and look at some better kits. Also, twin turbo and 600-1000 HP is quite serious and there would need to be a lot of supplementary supporting work done to handle it if you're serious about those levels of HP.
Good luck!
~Epyon