Ceramic impellers are sure cheaper to make than steel ones. Im not aware of any turbos that use a 2 piece combination as it is just one single shaft through the turbo. All the turbos of the RB series engines where all ceramic bladed turbos. The GTR's were the exception though. they had steel units though dont quote me on it.

HDI which are chinease actually make the better intercoolers on the market even better than those of trust, hks and the like in most cases.

If they arent ball bearing units they are just the normal floating type which are a lot more prone to shaft play and coking of the turbo which may explain why they offer a turbo timer.