How old is the legria hf r57 and how does it compare to the newest models

[Rud]

I've seen this model going cheap and I can't really find out much about it. I can't find out which model it's been replaced by etc.

[VideoGeek]

It appears the latest models of the LEGRIA are the HF R66 and HF R68.  The major difference between those two appears to be the that the Wide Attachment lens is included on the R68 and not the R66. 

Specs for each can be found in the following links:

LEGRIA HF R56/R57/R506

LEGRIA HF R66

Canon LEGRIA HF R68

I hope this helps.