They take a bit of fetteling as they are a different shape from the original ones. The plastic unit is oval shaped and the alloy more rectangular so you need to increase the size of the recess with a craft knife or scalpel.
The mechanism is also slightly different as the plastic ones are fully enclosed but the alloy ones have a bit that extends out when you pull on it and you need to get your dremel out and neatly remove it.
Finally original units use two small screws and the alloy have a single centrally located fixing so you need to drill through the wheel to mount.
I would strongly reccomend a wheel upgrade though, as for me the wheel was skinny and cheap feeling and this wasnt limited to the paddles. See my listing