OK, I'll chime in here, I guess I've been away too long.
Quaife makes valid points regarding the steel vs. iron housing, as well as the increase in pinion gears. Regarding the housing issue, generally speaking, parallel axis gear differentials have an unbalanced load on their planet (pinion) gears, and this causes them to "tip" into the housing. This puts a vary high (and unequally distributed) load on the housing bores that the gears are located in. Because of this, these units generally need the properties of a steel housing to have durability over life.
A Torsen Type-2 differential uses a planet gear design that has much better load balancing (which is something we've patented), so as a result, the load on the housing is less, and thus the normal need for steel is gone. As a result, we can design and build units used in high performance applications and still maintain good durability.
Regarding the number of pinions, well, the balanced gear design also doubles the tooth transfer area on the pinions compared to typical designs, which is often the failure mode in this type of applications. It does not, however, increase contact with the side gears, so he's got me there.
Again, I can make a point of having increased torque bias ability, which is why FRPP choose our product over "the competition's" after testing both. So, yes, at this point, it is a matter of both companies believing they have the better product. Which is better? It may, in the end, not make a great deal of difference, its what the customer prefers. There are advantages and disadvantages to both, as was said above...
Oh, I don't know about what machining is required for the Quaife, if any (as was asked above), but I can say that the Torsen has the same mounting dimensions as the stock differential, so it is drop in.
