I bought these along with new C-hubs (#MIF019B), and they are really good and accurate. The advantage with aluminium rather than plastic is that the screw threads are much better on aluminium. They are relatively easy to install if you know how things are screwed together on a Mini Inferno.
It is highly recommended to use some kind of thread locker on the screws that attaches the steering block to the C-Hub, because they tend to screw themselves out when you turn a lot.
After I applied thread locker and let it dry, I've had no problems whatsoever with this product!
Highly recommended for precision and durability!