Circular Saw Models...

[ag54]

I purchased a combo kit a while back and the circular saw has a model number of R845. I just purchased another kit off eBay and that circular saw is model R8452.

There are two noticeable differences, one the guide handle of the R845 has a rubber grip and it also has a metal blade shield... the R8452 does not have the grip and has a plastic shield.

My questions follow:

Assuming the R8452 is a newer model...

Are there any other differences (Quality, performance...)?
Why would they go from a metal shield to a plastic one?

Thanks for any help!
AG