[Finnster]

The think I like about the Cens are the spider gears are much harder and stronger than the HPI ones. The pinion and ring are cast tho, and not machined like the HPIs.
The diff ratios are different as well. You shouldn't need to shim the HPIs so much like the CENs then also.
Depends on all you are looking for, but the new HPI gears are a very welcome upgrade