When I was building my Cadtrac I considered buying some components from Metkit. After some serious research I decided against it. At the time they were buying lots of hydraulic and mechanical parts from manufacturers in hopes of selling them to the end customers as part of a kit or as individual components.
The problem was they weren't considered a wholesaler by many of the manufacturers. As a result items like hydraulic cylinders and motors were considered as sold to the end user when Metkit bought them. The warranty started in the day they took possession.
There were cases where Metkit customers bought items who's warranty time had run out while they were setting on the shelves. A few had the unpleasant experience of having component failure only to find out the warranty had expired before they even took possession. The manufacturer refused to do anything and at the time Metkit also balked. I don't know if Metkit finally made good on the defective items, or whether the end customer was just plain out of luck.
Metkit prices were considerably higher than buying identical components from hydraulic, and steel suppliers. If you were looking for a quick build Metkit did offer a complete kit with all the steel components pre-cut, and the hydraulic components matched and pre packaged. Personally I opted to source my own components and saved a considerable amount of money doing so.